Wildlife Monographs

Published by Wiley
Online ISSN: 1938-5455
Print ISSN: 0084-0173
Model averaged estimates of apparent survival of territorial female northern spotted owls in 4 study areas in Washington (a), 6 study areas in Oregon (b), and 4 study areas in California (c).
Estimates of apparent survival rates of adult female northern spotted owls in 6 geographic regions from the meta-analysis of 14 study areas and based on model f/ (region þ t) p(g þ t þ s)g.
Figure F.1. Histograms for study areas in Washington comparing habitat suitability scores for all lands inside the demographic study areas (DSA), for federal lands (Fed Land) outside the study area in the province, and for nonfederal lands (Pvt Land) in the province. 
We analyzed demographic data from northern spotted owls (Strix occidentalis caurina) from 14 study areas in Washington, Oregon, and California for 1985–2003. The purpose of our analyses was to provide an assessment of the status and trends of northern spotted owl populations throughout most of their geographic range. The 14 study areas made up approximately 12% of the range of the subspecies and included federal, tribal, private, and mixed federal and private lands. The study areas also included all the major forest types that the subspecies inhabits. The analyses followed rigorous protocols that were developed a priori and were the result of extensive discussions and consensus among the authors. Our primary objectives were to estimate fecundity, apparent survival (ϕ), and annual rate of population change (λ) and to determine if there were any temporal trends in these population parameters. In addition to analyses of data from individual study areas, we conducted 2 meta-analyses on each demographic parameter. One meta-analysis was conducted on all 14 areas, and the other was restricted to the 8 areas that constituted the Effectiveness Monitoring Plan for northern spotted owls under the Northwest Forest Plan. The average number of years of reproductive data per study area was 14 (range = 5–19), and the average number of recapture occasions per study area was 13 (range = 4–18). Only 1 study area had <12 years of data. Our results were based on 32,054 captures and resightings of 11,432 banded individuals for estimation of survival and 10,902 instances in which we documented the number of young produced by territorial females.
We assessed the effectiveness of an extensive and unprecedented wildlife reduction effort directed at a wide-ranging migratory population of geese. Population reduction efforts that targeted several populations of light geese (greater snow geese [Chen caerulescens atlantica], lesser snow geese [C. c. caerulescens], and Ross's geese [C. rossii]) began in 1999 in central and eastern North America. Such efforts were motivated by a broad consensus that abundance of these geese was causing serious ecological damage to terrestrial and salt marsh ecosystems in central and eastern parts of the Canadian Arctic and subarctic regions along Hudson Bay. Starting in February 1999, special conservation measures (or, in the U.S., a conservation order) were added to the respective federal regulations that permitted hunters to take snow geese (in parts of Canada and the U.S.) and Ross's geese (in parts of the U.S.) during specified harvest periods outside of the hunting season. These measures were accompanied by increase or removal of daily kill and possession limits and by permissions to use previously prohibited equipment for hunting these species in certain regions of the continent. The intent was to reduce adult survival through increased hunting mortality, which was judged to be the most cost-effective approach to reversing population growth. Our principal goal was to assess the effectiveness of reduction efforts directed at the midcontinent population of lesser snow geese, which was thought to be the most serious threat to arctic and subarctic ecosystems of the 3 light goose populations. Our multiple objectives included the estimation and detection of change in the response measures of total annual harvest, harvest rate, survival rate, and abundance, using the 1998 hunting period (defined as 1 Aug 1998 to 31 Jul 1999) as a point of reference. We used information about hunter recoveries of leg-banded snow geese and estimates of regular-season harvest to estimate 1) conservation-order harvest and total annual harvest, 2) geographic and temporal distribution of recoveries by age class, 3) survival and recovery probability, and 4) abundance of snow geese each August using Lincoln's (1930) method. We also modeled population growth to infer the form of population response to management efforts. Toward that end, we also proposed a method of estimating conservation-order harvest and tested for differences in band-reporting rate between Canada and the United States. Overall, the balance of evidence favored the conclusion that the midcontinent population has continued to grow during the conservation order, although perhaps at a reduced rate. We suggest that annual rate of population growth , derived from estimates of annual population size in August, likely provides the most reliable inference about change in the midcontinent population. There was a decline in annual survival probability between these 2 periods from about 0.89 to about 0.83 among snow geese from the southern-nesting stratum (south of 60°N latitude), thought to compose about 10% of the midcontinent population. However, we detected no change in the much larger northern-nesting stratum (north of 60°N latitude), where annual survival remained at about 0.87 from 1989 to 2006. Thus, the conclusion that this population continued to increase during the conservation order was largely consistent with the finding that a weighted-survival probability for midcontinent snow geese essentially did not change between the period preceding (1989–1997) and during (1998–2006) the conservation order. Consistent with high survival rates were low harvest rates, which increased from 0.024 during 1989–1997 for northern geese to only 0.027 during 1998–2006 and from 0.031 to only 0.037 for southern geese. Despite the initial increase associated with the conservation order, harvest rates declined during the conservation order for geese from both strata. We suggest that the higher harvest rate evident for southern geese was related to their earlier fall migration and thus earlier exposure to harvest pressure. Migration by more abundant northern geese was later and resulted in a higher ratio of geese to hunters. Additionally, there was more harvest of southern geese in areas north of the Canadian prairies than there was of northern geese. Total annual harvest increased due to the conservation order but failed to exceed 0.75 million adults in any year during the assessment from 1989 to 2006. Harvest of both age classes exceeded 1 million in only 2 of 9 annual harvest periods since the conservation order started. These lower-than-expected harvests of adult snow geese combined with their low harvest rates of ≤0.048 during the conservation order suggested an August population size in excess of 15 million adult snow geese since 1998. We suggest that abundance of midcontinent snow geese was seriously underestimated in the past, and that this underestimate may have contributed to an overconfidence with which suggested harvest levels could achieve a goal of reduced survival and population reduction. Overall, all 3 populations of light geese now exceed numbers present when the conservation order was initiated. We are confident that the abundance and population growth rate of midcontinent snow geese (as well as by Ross's and greater snow geese) currently exceeds the ability of existing numbers of hunters to exert harvest pressure that is necessary to impose sufficient additive mortality and thus effectively influence population growth. It remains unknown how much more or how much longer such populations can increase towards carrying capacity, which we assume to be determined by the standing crop of arctic foods that they exploit, before density dependence can measurably slow the population growth rate. Estimation of carrying capacity in the large northern nesting stratum is among the key research needs that we propose. The situation that has emerged requires a review of perspectives about impacts of midcontinent lesser snow geese in the arctic, whether initial goals behind population management are still relevant, and whether alternative options from the initial array of management tools should be exercised. © The Wildlife Society, 2011Nous avons évalué l'efficacité d'un effort étendu et sans précédent de réduction d'une espèce sauvage, une population migratrice d'oies occupant une large étendue géographique. Les efforts de réduction de populations ciblant plusieurs populations d'oies blanches (grande oie des neiges, Chen caerulescens atlantica, petite oie des neiges, C. c. caerulescens, et oie de Ross, C. rossii) ont débutés en 1999 dans le centre et l'est de l'Amérique du Nord. Ces efforts étaient justifiés par un consensus élargi à l'effet que ces oies causaient des dommages écologiques aux écosystèmes terrestres et de marais salés dans les régions centrales et orientales de l'Arctique Canadien ainsi que dans les régions subarctiques le long de la Baie d'Hudson. À partir de 1999, des mesures de conservation spéciales (décret de conservation aux É.U.) furent ajoutées aux règlements fédéraux respectifs qui permettaient aux chasseurs de récolter des oies des neiges (dans certaines régions du Canada et des É.U.) et des oies de Ross (dans certaines régions des É.U.) pendant des périodes de récolte spécifiques, hors de la saison de chasse. Ces mesures étaient accompagnées d'une augmentation ou de l'élimination des limites de prises quotidiennes et de possession, ainsi que l'autorisation d'utiliser des engins de chasse précédemment prohibés pour la chasse de ces espèces dans certaines régions du continent. L'intention était de réduire la survie des adultes par l'entremise d'une augmentation de la mortalité par la chasse, approche jugée comme étant la plus efficace pour inverser la croissance de la population. Notre objectif principal était d'évaluer l'efficacité des efforts de réduction dirigés vers la population de la petite oie des neiges du milieu du continent, qui était considérée come étant la plus grande menace aux écosystèmes arctiques et subarctiques des 3 populations d'oies blanches. Les multiples objectifs de ce manuscrit incluent l'estimation et la détection de changements dans les mesures de récolte annuelle totale, de taux de récolte, de taux de survie et d'abondance, utilisant la période de chasse de 1998 (définie comme étant du 1 août 1998 au 31 juillet 1999) comme point de référence. Nous avons utilisé de l'information sur les retours, par les chasseurs, de bagues d'oies des neiges ainsi que des estimés de la récolte durant la saison régulière pour estimer: (1) la récolte pendant les périodes du décret de conservation et la récolte annuelle totale, (2) la distribution temporelle et géographique des retours de bagues par classe d'âge, (3) la survie et la probabilité de retour de bague et (4) l'abondance des oies des neiges à chaque mois d'août en utilisant la méthode de Lincoln (1930). Nous avons aussi modélisé la croissance de la population afin de déduire la forme de la réponse de la population aux efforts de gestion. À cette fin, nous avons aussi proposé l'utilisation d'une méthode pour estimer la récolte pendant les périodes couvertes par le décret de conservation et avons testé pour des différences dans les taux de signalement de bagues entre les États-Unis et le Canada. Dans l'ensemble, l'évidence suggère que la population du milieu du continent a continué de croître durant la période du décret de conservation, mais possiblement à un taux moins élevé. Nous suggérons que le taux de croissance de la population, , estimé à partir des estimés de taille de population annuelle en août, prodigue probablement les inférences les plus fiables sur les changements dans la population du milieu du continent. Il y a eu un déclin de la probabilité de survie annuelle entre ces deux périodes, d'environ 0,89 à environ 0.83, pour les oies des neiges nichant dans la strate sud (sud de la latitude 60°N) et qui représentent environ 10% de la population du milieu du continent. Par contre nous n'avons détecté aucun changement dans la plus imposante strate nordique (nord de la latitude 60°N) où la survie annuelle est demeurée aux environs de 0.87 pour la période 1989 à 2006. La conclusion que cette population a continué d'augmenter pendant la période du décret de conservation concorde avec le résultat qui indique que la probabilité de survie pondérée pour l'ensemble de la population du milieu du continent n'as pas changé entre la période précédent (1989–1997) et celle durant (1998–2006) le décret de conservation. Les taux de survie élevés concordaient avec de faibles taux de récolte, qui ont augmenté de 0.024 pendant 1989–1997 pour les oies de la strate nord à seulement 0.027 pendant 1998–2006, et de 0.031 à seulement 0.037 pour les oies de la strate sud. Malgré une augmentation initiale associée au décret de conservation, les taux de récolte ont déclinés pendant la période couverte par le décret de conservation dans les deux strates. Nous suggérons que les taux de récolte plus élevés pour les oies de la strate sud sont dus à leur migration automnale plus hâtive, ce qui les exposerait plus tôt à la pression de chasse. La migration des oies de la strate du nord, plus abondantes, avait lieu plus tard et résultait en un ratio d'oies par chasseurs plus élevé. De plus, il y avait une plus grande récolte d'oies de la strate sud dans les secteurs au nord des prairies Canadiennes que pour les oies de la strate nord. La récolte annuelle totale a augmenté suite au décret de conservation mais n'as excédé 0.75 million d'adultes dans aucune des années utilisées dans l'évaluation, soit de 1989 à 2006. La récolte des deux classes d'âge à dépassé 1 million pour seulement 2 périodes de récolte annuelles sur 9 depuis la mise en place du décret de conservation. Cette récolte plus faible que prévue d'oie des neiges adulte et le faible taux de récolte de ≤ 0.048 pendant la période du décret de conservation laisse croire que la population, mesurée au mois d'août, aurait été de plus de 15 millions d'adultes depuis 1998. Nous suggérons que l'abondance de la population d'oie des neiges du milieu du continent a été sérieusement sous-estimée dans le passé et que cette sous-estimation pourrait avoir contribué à un sentiment de sur-confiance envers le fait que les niveaux de récolte pourraient mener à l'atteinte de l'objectif de diminution de la survie et réduction de la population. Les 3 populations d'oies blanches ont maintenant des populations plus grandes que lors de la mise en place du décret de conservation. Nous somme convaincus que l'abondance et le taux de croissance actuel de la population d'oie des neiges du milieu du continent (ainsi que l'oie de Ross et la grande oie des neiges) dépasse la capacité des chasseurs actifs d'exercer une pression de récolte suffisante pour augmenter la mortalité additive à un niveau qui influencerait effectivement la croissance de la population. Nous ne savons toujours pas pendant combien de temps ces populations peuvent continuer de croître et approcher la capacité de support, que l'on pense déterminée par la population sur pied des plantes arctiques qu'elles exploitent, avant que des effets densité-dépendants ralentissent le taux de croissance de la population de façon mesurable. L'estimation de la capacité de support de la grande strate du nord est un des besoins clés en recherche que nous proposons. La situation qui émerge requière une revue des perspectives concernant les impacts des oies des neiges du milieu du continent dans l'Arctique, si les objectifs initiaux de gestion de la population sont encore pertinents et si d'autres options à partir de l'ensemble initial d'outils de gestion doivent être exercées.Investigamos la efectividad de una iniciativa de disminución de vida silvestre bastante extensiva y sin antecedentes, dirigida a una población migratoria de gansos blancos de un amplio rango de distribución. En 1999, se iniciaron esfuerzos de disminución de poblaciones dirigidos a varias poblaciones de gansos claros (Chen caerulescens atlantica, C. c. caerulescens, y C. rossii) en las regiones centrales y del este de Norte América. Estos esfuerzos fueron motivados por el amplio consenso sobre la noción de que la abundancia de estos gansos estaba causando graves daños ecológicos a ecosistemas terrestres y humedales salobres en las regiones centrales y del este del Ártico Canadiense y las regiones sub-árticas a lo largo de la Bahía Hudson. Medidas especiales de conservación (definidas en E.E.U.U. como una “orden de conservación”) fueron añadidas en Febrero de 1999, a las regulaciones federales respectivas, las cuales les permiten a los cazadores cazar gansos blancos (en partes de Canadá y E.E.U.U.) y gansos de la especie C. rossii (en partes de E.E.U.U.) durante periodos específicos de cosecha fuera de la temporada de cacería regular. Estas medidas fueron acompañadas por un aumento y/o remoción de límites de posesión y matanza diaria, al igual que permisos para utilizar equipo prohibido anteriormente para la cacería de estas especies en ciertas regiones del continente. La intención era disminuir la supervivencia de adultos por medio de un aumento en la tasa de mortalidad como resultado de la cacería, la cual fue designada como la forma más rentable para poner en marcha atrás el crecimiento poblacional. Nuestra meta principal fue asesorar la efectividad de los esfuerzos de disminución dirigidos a las poblaciones de C. c. caerulescens en el continente medio, la cual, de las tres poblaciones de gansos blanco, se considera que presenta la amenaza más seria a los ecosistemas árticos y sub-árticos. Los objetivos múltiples de este artículo incluyen la estimación y detección de cambios en las medidas de respuestas de cosecha anual total, tasa de cosecha, tasa de supervivencia, y abundancia, utilizando el periodo de cacería de 1998 (definido como el 1 de Agosto 1998 al 31 de Julio 1999) como el punto de referencia. Utilizamos información sobre individuos de gansos blancos anillados en una pata que fueron recuperados por cazadores y valores estimados de cosechas durante la temporada de cosecha regular, para estimar (1) cosecha durante la orden de conservación y la cosecha anual total, (2) distribución geográfica y temporal de individuos recuperados por clase de edad, (3) probabilidades de supervivencia y recuperación, y (4) abundancia de gansos blancos para cada mes de Agosto utilizando el método de Lincoln (1930). También modelamos el crecimiento poblacional para realizar inferencias sobre la forma de la respuesta poblacional a las iniciativas de manejo. Para este fin, también proponemos metodología para estimar la cosecha durante la orden de conservación y realizamos pruebas para determinar si existen diferencias entre tasas de reportaje de anillos entre Canadá y E.E.U.U. En conjunto, la evidencia favorece la conclusión de que la población del continente medio ha continuado de crecer durante la orden de conservación, aunque tal vez a una tasa más reducida. Sugerimos que la tasa anual de crecimiento poblacional, , estimada a partir de valores estimados de tamaño poblacional anual en Agosto, probablemente proporcionan el nivel de inferencia más confiable sobre cambios de la población del continente medio. Tuvimos una disminución en la probabilidad de supervivencia anual entre estos dos periodos, desde alrededor de 0.89 hasta alrededor de 0.83 entre gansos blancos del estrato de anidamiento sureño (sur de 60°N latitud), los cuales se consideran que componen alrededor de 10% de la población del continente medio. No obstante, detectamos que en el estrato de anidamiento norteño (norte de 60°N latitud), cuya población es mucho más grande, no hubieron cambios, y supervivencia permaneció a valores alrededor de 0.87 desde 1989 hasta 2006. En consecuencia, la conclusión de que esta población continúo aumentando durante la orden de conservación es bastante consistente con nuestro descubrimiento que una probabilidad de supervivencia ponderada para los gansos blancos del continente medio esencialmente no cambio entre el periodo precedente (1989–1997) y durante (1998–2006) la orden de conservación. Las tasas altas de supervivencia resultaron consistentes con tasas de bajas cosecha, las cuales aumentaron de 0.024 durante 1989–1997 para gansos norteños a solo 0.027 durante 1998–2006, y de 0.031 a solo 0.037 para gansos sureños. A pesar del aumento inicial asociado con la orden de conservación, tasas de cosecha disminuyeron durante la orden de conservación para gansos de ambos estratos. Sugerimos que las tasas de cosecha elevadas que fueron evidentes en gansos sureños estaban relacionadas a su época de migración más temprana durante el otoño, y por ende, estos fueron expuestos a una presión de cosecha más temprano. La migración de los gansos norteños más abundantes se realizo después y resulto en una proporción más alta de gansos a cazadores. Adicionalmente, se cosecharon más gansos sureños en regiones ubicadas al norte de las praderas de Canadá que se cosecharon gansos norteños. La cosecha total anual aumento a causa de las acciones de conservación, pero falló en exceder los 0.75 millones de adultos para cualquier año al que este fue asesorado, del 1989 al 2006. La cosecha de ambas clases de edades excedió 1 millón para solo 2 de los 9 periodos de cosecha desde que la orden de conservación inició. La combinación de una cosecha de adultos de ganso blanco por debajo de lo esperado y las bajas tasas de cosecha de ≤ 0.048 durante la orden de conservación nos indican que hemos tenido un exceso de 15 millones de gansos blancos sobre el tamaño poblacional para el mes de Agosto desde 1998. Sugerimos que la abundancia de gansos blancos del continente medio fue seriamente subestimada en el pasado, y que esta subestimación posiblemente contribuyo al exceso de confianza que se tuvo de que los niveles de cosecha sugeridos podrían lograr los objetivos de disminuir supervivencia y reducir la población. En general, las tres poblaciones de gansos blancos en este estudio ahora exceden las cantidades presentes cuando la orden de conservación inició. Estamos confidentes de que la abundancia y la tasa de crecimiento poblacional del ganso blanco del continente medio (al igual para C. c. atlántica y C. rossii) actualmente exceden la presión de cosecha que puede ejercer la cantidad de cazadores existentes requerida para imponer niveles suficientes de mortalidad aditiva, y por ende, influir efectivamente niveles de crecimiento poblacional. Todavía no sabemos que tanto mas podrían aumentar dichas poblaciones hacia la capacidad de carga, ni por cuanto más tiempo, lo cual presumimos que se podría determinar basándose en la cantidad existente de fuentes alimenticias en el ártico que ellos puedan explotar, antes de que la dependencia de densidad pueda reducir la tasa de crecimiento poblacional. La estimación de la capacidad de carga del amplio estrato de anidamiento ubicado en el Norte es justo uno de los objetivos claves de investigación que proponemos. La situación que tenemos antemano requiere de un repaso de las perspectivas sobre los impactos de C. c. caerulescens del continente medio, determinar si los objetivos de manejo de poblaciones iniciales todavía son relevantes, y ver si debemos optar por opciones alternativas que no son parte del conjunto inicial de herramientas de manejo.
ABSTRACT  Our understanding of wolf (Canis lupus) population dynamics in North America comes largely from studies of protected areas, at-risk populations, and wolf control programs, although most North American wolves experience moderate levels of regulated harvest. During 1986–1992, we investigated the population dynamics and harvests of wolves in the newly created Gates of the Arctic National Park and Preserve in northern Alaska, USA, where wolves were harvested by local residents. Our objectives were to determine wolf abundance, estimate important vital rates (i.e., productivity, survival, emigration), and characterize wolf harvests. We monitored 50 radiocollared wolves in 25 packs over 4 years (Apr 1987–Apr 1991) to assess patterns of dispersal, emigration, survival and mortality causes in the wolf population. We determined pack sizes, home ranges, and pups per pack in autumn (1 Oct) for instrumented wolf packs, and calculated wolf densities in autumn and spring (15 Apr) based on the number of wolves in instrumented packs and the aggregate area those packs inhabited. We also gathered information from local hunters and trappers on the timing, location, methods, and sex-age composition of wolf harvests during 6 winter harvest seasons (Aug 1987–Apr 1992).Wolf densities averaged 6.6 wolves per 1,000 km2 and 4.5 wolves per 1,000 km2 in autumn and spring, respectively, and spring densities increased by 5% per year during our study. On average, pups constituted 50% of the resident wolf population each autumn. An estimated 12% of the population was harvested annually. Natural mortality, primarily intraspecific strife, equaled 11% per year. Young wolves emigrated from the study area at high annual rates (47% and 27% for yearlings and 2-yr-olds, respectively), and we estimated the emigration rate for the population at ≥19% annually. Yearlings and 2-year-olds were lost from the population at rates of 60% per year and 45% per year, respectively, primarily as a result of emigration; mortality was the principal cause of the 26% annual loss of wolves ≥3 years old.On average, 47 wolves were harvested each winter from our study population, or twice the harvest we estimated from survival analyses of radiocollared wolves (23 wolves/yr). We suggest that the additional harvested wolves were transients, including local dispersers and migrants from outside the study area. Trapping harvest was well-distributed throughout the trapping season (Nov-Apr), whereas shooting harvest occurred mainly in February and March. Of 35 individuals who harvested wolves in the area, 6 accounted for 66% of the harvest.We analyzed information from North American wolf populations and determined that annual rates of increase have an inverse, curvilinear relationship with human-caused mortality (r2 = 0.68, P < 0.001) such that population trends were not correlated with annual human take ≤29% (P = 0.614). We provide evidence that wolf populations compensate for human exploitation ≤29% primarily via adjustments in dispersal components (i.e., local dispersal, emigration, and immigration), whereas responses in productivity or natural mortality have little or no role in offsetting harvests. Given the limited effects of moderate levels of human take on wolf population trends and biases in assessing wolf populations and harvests resulting from the existence of transient wolves, the risks of reducing wolf populations inadvertently through regulated harvest are quite low.RESEMEN  Nuestra comprensión de la dinámica poblacional del lobo (Canis lupus) en Norteamérica procede sobre todo de estudios en áreas protegidas, de poblaciones amenazadas y de programas de control de lobos, aunque la mayoría de los lobos norteamericanos experimentan niveles moderados de explotación regulada. Durante 1986–1992, hemos investigado la dinámica poblacional y el aprovechamiento del lobo en el recientemente creado Parque Nacional y Reserva Gates of the Arctic, en el norte de Alaska, donde los lobos fueron explotados por los residentes locales. Nuestros objetivos han sido determinar la abundancia de lobos, estimar los parámetros vitales más importantes (productividad, supervivencia, emigración) y caracterizar la explotación de los lobos. Hemos seguido 50 lobos radiomarcados en 25 manadas durante 4 años (abril de 1987–abril de 1991) para conocer los patrones de dispersión, la emigración, la supervivencia y las causas de mortalidad de la población. Hemos determinado los tamaños de manada, las áreas de campeo y los cachorros/manada en otoño (1 de octubre) en las manadas con lobos marcados, y hemos calculado la densidad de lobos en otoño y primavera (15 de abril) considerando el número de lobos en las manadas controladas y la superficie total ocupada por dichas manadas. También hemos recogido información de cazadores y tramperos locales sobre la estacionalidad, localización, métodos y composición de sexo y edad de los lobos muertos en 6 periodos invernales de aprovechamiento (agosto de 1987–abril de 1992).La densidad media fue de 6,6 lobos/1.000 km2 y 4,5 /1,000 km2 en otoño y primavera, respectivamente, y las densidades en primavera aumentaron un 5% anual durante el estudio. De media, los cachorros constituyeron el 50% de la población residente cada otoño. Hemos estimado que cada año se extrajo el 12% de la población. La mortalidad natural, fundamentalmente por luchas intraespecíficas, alcanzó el 11% anual. Los ejemplares jóvenes del área de estudio presentaron elevadas tasas anuales de emigración (el 47% y el 27% para lobos de 1 a 2 años y de 2 a 3 años, respectivamente), y la tasa de emigración anual estimada para la población ha sido ≥19%. El 60% y el 45% de los lobos de 1 a 2 y de 2 a 3 años respectivamente desaparecieron cada año de la población, sobre todo a causa de la emigración; la mortalidad fue la principal causa de la pérdida del 26% anual de los lobos ≥3 años.De media, se extrajeron 47 lobos cada invierno en los programas de aprovechamiento en el área de estudio, es decir, el doble de la cifra que hemos estimado analizando la supervivencia de los lobos radiomarcados (23 lobos/año). Sugerimos que los restantes lobos extraídos eran transeúntes, incluyendo dispersants locales y migrantes de fuera del área de estudio. La extracción por trampeo estuvo bien distribuida a lo largo de la estación de trampeo (noviembre-abril), mientras que la extracción con armas de fuego se produjo sobre todo en febrero y marzo. De los 35 individuos que extrajeron lobos en la zona, 6 acapararon el 66% de las capturas.Tras analizar la información de las poblaciones norteamericanas de lobos, hemos determinado que las tasas anuales de aumento muestran una relación inversa y curvilinear con la mortalidad causada por el hombre (r2 = 0,68, P < 0,001), de tal forma que las tendencias de las poblaciones no estaban correlacionadas con la mortalidad humana cuando ésta fue ≤29% anual (P = 0,614). Aportamos pruebas de que, cuando las tasas anuales de explotación por el hombre son ≤29%, las poblaciones de lobos las compensan fundamentalmente ajustando los componentes de la dispersión (es decir, la dispersión local, la emigración y la inmigración), mientras que las respuestas en productividad o mortalidad natural tienen un papel escaso o nulo al compensar las extracciones. Considerando que unos niveles moderados de extracción por el hombre tienen un impacto limitado sobre la tendencia de las poblaciones de lobos y que existen sesgos en la estima de las poblaciones y en la extracción causados por la existencia de lobos transeúntes, los riesgos de reducir las poblaciones de forma inadvertida con un aprovechamiento regulado son bastante bajos.RÉSUMÉ  Notre compréhension de la dynamique des populations de loups (Canis lupus) d'Amérique du Nord provient grandement d'aires protégées, de populations menacées ou de programmes de contrǒle bien que la plupart des loups du continent subissent des niveaux d'exploitation modérés. Entre 1986 et 1992, nous avons étudié la dynamique des populations et la récolte de loups dans le nouveau parc national et la réserve Gates of the Arctic, au nord de l'Alaska, où les résidents locaux récoltaient des loups. Nos objectifs étaient de déterminer l'abondance des loups, d'estimer des taux d'évènements naturels importants (c-à-d. la productivité, la survie, l'émigration), et de caractériser la récolte de loups. À l'aide de colliers émetteurs, nous avons suivi, pendant 4 ans (avril 1987 à avril 1991), 50 loups appartenant à 25 meutes afin d'évaluer leurs patrons de dispersion, l'émigration, la survie et les causes de mortalité au sein de la population. Nous avons déterminé la taille des meutes, les domaines vitaux, et le nombre de louveteaux par meute en automne (1er octobre) pour les meutes comptant des loups marqués, et nous avons calculé les densités de loups en automne et au printemps (15 avril) d'après le nombre de loups par meute suivie et l'aire que ces meutes habitaient. Nous avons également recueilli des informations auprès des chasseurs et trappeurs locaux sur la chronologie, le lieu, les méthodes et la composition (sexe/ǎge) de la récolte de loups durant 6 saisons hivernales (aoǔt 1987 à avril 1992).Les densités moyennes de loups atteignaient 6,6 loups/1 000 km et 4,5 loups/1000 km2 en automne et au printemps, respectivement, et les densités printanières augmentèrent de 5% par année durant notre étude. En moyenne, les louveteaux représentaient 50% de la population résidente, chaque automne. Nous avons estimé la récolte annuelle moyenne à 12% de la population. La mortalité naturelle, principalement des conflits intraspécifiques, atteignait 11% par année. Les jeunes loups émigrèrent de l'aire d'étude à des taux élevés (47% et 27% pour les loups d'un an et de deux ans, respectivement) et nous avons estimé le taux d'émigration annuel pour l'ensemble de la population à ≥19%. Les loups d'un an et de deux ans disparaissaient de la population à des taux annuels de 60% et 45%, respectivement, principalement à cause de l'émigration; la mort était la principale cause de disparition des loups de 3 ans et plus qui quittaient la population chaque année (26%).En moyenne, 47 loups furent récoltés chaque hiver dans la population étudiée, soit 2 fois la récolte estimée par les analyses de survie des loups marqués (23 loups par an). Nous proposons que le surplus de loups récoltés provenait d'animaux de passage, incluant les loups locaux en dispersion et d'autres provenant de l'extérieur de l'aire d'étude. La récolte par piégeage s'étendait uniformément durant toute la saison (novembre à avril) alors que la récolte par la chasse se concentrait surtout en février et mars. Six des 35 personnes récoltant des loups dans l'aire d'étude étaient responsables à elles seules de 66% des prises.Nous avons analysé des données provenant de diverses populations de loups d'Amérique du Nord et trouvé que les taux d'accroissement possédaient une relation inverse et curvilinéaire avec les causes de mortalité induites par les humains (r2 = 0,68, P < 0,001) de telle sorte que les tendances démographiques n'étaient pas corrélées aux récoltes humaines (P = 0,614). Nous fournissons des évidences à l'effet que les populations de loups compensent pour l'exploitation humaine ≤29% principalement par l'entremise d'ajustements dans les facteurs de dispersion (c.-à-d. dispersion locale, émigration, immigration), alors que la productivité et la mortalité naturelle compensent peu ou pas du tout pour les récoltes. Étant donné les effets limités d'une récolte humaine modérée sur les tendances démographiques des populations de loups et les biais d'estimation des effectifs et des récoltes à cause de l'existence de loups de passage, les risques de reduction accidentelle de populations de loups résultant d'une récolte réglementée sont très faibles.
The Appalachian Cooperative Grouse Research Project (ACGRP) was a multistate cooperative effort initiated in 1996 to investigate the apparent decline of ruffed grouse (Bonasa umbellus) and improve management throughout the central and southern Appalachian region (i.e., parts of Ohio, Pennsylvania, Rhode Island, Kentucky, West Virginia, Virginia, and North Carolina, USA). Researchers have offered several hypotheses to explain the low abundance of ruffed grouse in the region, including low availability of early-successional forests due to changes in land use, additive harvest mortality, low productivity and recruitment, and nutritional stress. As part of the ACGRP, we investigated ruffed grouse population ecology. Our objectives were to estimate reproductive rates, estimate survival and cause-specific mortality rates, examine if ruffed grouse harvest in the Appalachian region is compensatory, and estimate ruffed grouse finite population growth. We trapped >3,000 ruffed grouse in autumn (Sep-Nov) and spring (Feb-Mar) from 1996 to September 2002 on 12 study areas. We determined the age and gender of each bird and fitted them with necklace-style radiotransmitters and released them at the trap site. We tracked ruffed grouse ≥2 times per week using handheld radiotelemetry equipment and gathered data on reproduction, recruitment, survival, and mortality.
Recent declines in numbers and juvenile recruitment in many elk (Cervus elaphus) herds in the western U.S. has sparked interest in factors that may cause these declines. Inadequate nutrition or delayed parturition, the latter of which may be caused by inadequate numbers of mature bulls (i.e., highly skewed sex ratios), may have separate or synergistic effects on population dynamics and productivity. We evaluated the implications of late parturition and summer-autumn nutrition on reproduction and survival of Rocky Mountain elk (C. e. nelsoni) using a captive herd of 57 cow elk.We induced early (Sep) and late breeding (Oct) and 3 levels of summer-autumn nutrition on the cows. Food was offered ad libitum at 3 levels of digestible energy (DE): high = 2.9-3.0 kcal of DE/g of diets, medium = 2.6-3.0 kcal/g, and low = 2.3-3.0 kcal/g. Within these ranges, DE content was gradually reduced from late June through early November to mimic seasonal changes in the wild. During summer and autumn, we measured calf growth; body mass, nutritional condition, and breeding dynamics of cows; and growth and pregnancy of yearlings. We also measured carry-over (i.e., time-lag) responses including over-winter calf and cow survival and parturition date and birth mass, as functions of previous summer-autumn nutrition and previous parturition date. Between autumn 1995 and spring 1998, we conducted 2 years of parturition-date, summer-autumn nutrition experiments, 2 winters of calf survival experiments, and 1 winter of cow survival experiments.Early birth provided calves with more time to grow before onset of winter. This “head-start” advantage was maintained through late autumn, but its magnitude was diluted in some instances due to faster growth of some late-born calves. Body mass, body fat, and timing and probability of conception by cows in autumn were little influenced by parturition date the previous spring.Summer-autumn nutrition significantly affected calves and their mothers. Growth of calves in the low and medium nutrition groups ceased by mid-September and late October. By December, calves in the high nutrition group were 40% and 70% heavier than calves in the medium and low groups, respectively. Cows in the high nutrition group accumulated about 75% and 300% more fat than cows in the medium and low groups by mid-October. Eighty percent of cows in the low nutrition group failed to conceive, and those in the medium group bred 10–14 days later than cows in the high group. Summer-autumn nutrition of calves influenced their probability of becoming pregnant as yearlings. Probability of pregnancy approached 100% for those yearlings that had high summerautumn nutrition as calves and yearlings, despite near starvation their first winter of life.Winter survival of calves was related to their size at the onset of winter. Smaller calves lost more body mass daily than did large calves, and thus they survived fewer days through winter. Summer-autumn nutrition largely determined calf body size at the start of winter and, consequently, determined the proportion of winter survived. Survival of cows over winter was as related to body fat at the onset of winter as it was to nutrition during winter.Carry-over effects of summer-autumn nutrition and parturition date on birth characteristics the following spring were minor. We detected no significant carry-over effect of summer-autumn nutrition or autumn condition on birth mass, although reduced condition in autumn delayed subsequent parturition date. Extent of body fat depletion in cows during the winter-survival experiments in 1998 accounted for 45% of the variation in parturition date. Ninety percent depletion delayed parturition an average of 34 days.Delayed parturition, of a magnitude expected due to highly skewed sex ratios (3 weeks under extreme conditions), probably has only a weak influence on vital rates of free-ranging elk. In contrast, fat accretion and probability of pregnancy of cows, and growth and overwinter survival of calves, were sensitive to small (10–20%) differences in DE content of food. Digestible energy levels of our 2 lower nutrition levels reflect DE ranges reported for large ungulate herds during summer and autumn in western North America. Thus, our data suggest that limiting effects of summer-autumn nutrition on populations may be greater than often assumed, perhaps greater than those during winter in some ecosystems, and consequently indicate a need for greater understanding of nutrition's influence on population dynamics and how this influence varies across space and time. To enhance future research, we present animal- and vegetation-based guidelines for evaluating nutritional influences on elk populations.
The population status of the Florida black bear (Ursus americanus floridanus) is problematic within many portions of its range and its potential listing as a federally threatened species has been the subject of legal debate. We studied Florida black bears in 2 areas in the Okefenokee-Osceola ecosystem in southeast Georgia (i.e., Okefenokee) and north Florida (i.e., Osceola) from 1995 to 1999 to evaluate relationships between population characteristics, habitat conditions, and human activities. Bears in Okefenokee were hunted and those in Osceola were not. We captured 205 different black bears (124M:81F) 345 times from June 1995 to September 1998. We obtained 13,573 radiolocations from 87 (16M:71F) individual bears during the study.In Okefenokee, black gum (Nyssa sylvatica) and saw palmetto (Serenoa repens) fruits were the most important foods for bears based on scat analysis. In Osceola, corn from white-tailed deer (Odocoileus virginianus) feeders was the most stable food source but saw palmetto was heavily used when available. Corn from deer feeders was not available in Okefenokee. Adult bears in Osceola were 29% heavier than those in Okefenokee (t82 = 3.55, P < 0.001).The mean annual home-range size for Osceola females (x = 30.3 km2 ± 4.0 [SE], n = 53) varied little seasonally or annually and was almost half that of Okefenokee females (55.9 km2 ± 6.9, n = 69; Z = −2.47, P = 0.014). In contrast, radiocollared females in Okefenokee expanded their home ranges during years of poor black gum production. That expansion was most apparent between autumn 1998 and 1999, when mean home-range size for Okefenokee females increased from 14.5 km2 to 78.4 km2, respectively, and included a larger proportion of upland areas open to sport hunting. As a result, 5 females were harvested in the Okefenokee study area during the 1999 bear hunting season compared with only 7 harvested from 1996 to 1998.Home ranges of adult female bears were located in areas with disproportionately high loblolly bay (Gordonia lasianthus) and gum-bay-cypress (Taxodium spp.) vegetation associations in Okefenokee and gum-bay-cypress associations in Osceola. The pine vegetation association ranked lower than most other associations within the home ranges of bears in both study areas even though much of the summer and autumn diets of bears included food items found almost exclusively in pine.Sixteen mortalities of radiocollared bears were documented in Okefenokee; hunting accounted for 11 (68.8%) of these deaths. The annual survival rate of radiocollared males in Okefenokee was 0.71 (95% CI = 0.53-0.88) whereas survival of females in Okefenokee was higher (Z = 18.87, P < 0.001) at 0.89 (95% CI = 0.83-0.95). The survival rate for females in Osceola was 0.97 (95% CI = 0.92-1.00). Overall, 67 bears (51M:16F) were killed by hunters in the Okefenokee study area from 1995 to 1999. Based on all radiocollared bears in Okefenokee, many of which resided within areas closed to hunting, we estimated an annual harvest rate of 0.22 (95% CI = 0.03-0.37) for males and 0.07 (95% CI = 0.01-0.12) for females. When we excluded those bears that were not in areas open to hunting, however, the annual harvest rate rose to 0.37 (95% CI = 0.07-0.58) for males and 0.39 (95% CI = 0.09-0.58) for females.Following a black gum shortage in autumn 1995, only 1 of 15 radiocollared females in Okefenokee produced cubs in winter 1996. That low reproductive rate was in contrast to winter 1997, which followed heavy black gum production, when 21 of 22 radiocollared females produced cubs. Reproductive output was more consistent in the Osceola study area, with 46 cubs being produced from 8, 5, and 9 litters in 1997, 1998, and 1999, respectively.To estimate population size, we maintained 88 and 94 barbed-wire hair traps during 1999 in the Okefenokee and Osceola study areas, respectively. Using DNA collected at the hair traps, mark-recapture models produced estimates of 71 bears (95% CI = 59–91) in Okefenokee and 44 bears (95% CI = 40–57) in the Osceola study area during 1999. The estimated densities in the Okefenokee and Osceola study areas were 0.12 and 0.14 bears/km2, respectively. Alternative density estimates based on the amount of time bears spent within study area boundaries were similar (0.11 and 0.14 bears/km2 on Okefenokee and Osceola, respectively).We used a population model to estimate the effect of harvest in the Okefenokee bear population. Excluding harvest, bears at Osceola experienced higher average annual population growth (Λ = 1.184 ± 0.002) than those at Okefenokee (1.064 ± 0.002; t18 = 3.93, P = 0.001), most likely due to protection from hunting and higher recruitment. Including the effects of emigration and immigration, we estimated an average annual sustainable harvest at Okefenokee of approximately 9 bears (12.6%), which was slightly less than the average 1995–1999 annual harvest of 9.4. That level of hunting in Okefenokee is sustainable but likely represents the highest exploitation rate in the region. Our mark-recapture data from Osceola suggest a high dispersal rate by subadult bears, and our population modeling data support this hypothesis; we documented bears in Okefenokee that originated from Osceola but not the reverse. We speculate that bears from the interior of the Okefenokee National Wildlife Refuge (ONWR), and to some extent northern Florida, served as a source to the population sink caused by hunting mortality in Okefenokee and in the surrounding Georgia counties.Corn from deer feeders was the most probable reason for smaller home-range sizes and greater body masses and reproductive output at Osceola. Changes in management to eliminate or reduce baiting for deer with corn would negatively affect the Osceola bear population. On Okefenokee, sporadic black gum and palmetto production influenced harvest rates and cub production and, thus, governed bear population dynamics.The U.S. Fish and Wildlife Service (USFWS) concluded in 1998 that listing the Florida black bear as threatened under the Endangered Species Act of 1973 was not warranted. That decision was largely based on the stability and protection afforded to a few subpopulations within the range of the subspecies, which includes the Okefenokee-Osceola subpopulation; our results support that conclusion. However, we suggest that metapopulation processes among the various subpopulations be given greater consideration, with the ultimate goal of managing the subspecies as a unit rather than as an assemblage of independent components. Our study illustrates the importance of travel corridors for maintaining metapopulation processes.
During the past 2 decades, the grizzly bear (Ursus arctos) population in the Greater Yellowstone Ecosystem (GYE) has increased in numbers and expanded in range. Understanding temporal, environmental, and spatial variables responsible for this change is useful in evaluating what likely influenced grizzly bear demographics in the GYE and where future management efforts might benefit conservation and management. We used recent data from radio-marked bears to estimate reproduction (1983–2002) and survival (1983–2001); these we combined into models to evaluate demographic vigor (lambda [λ]). We explored the influence of an array of individual, temporal, and spatial covariates on demographic vigor.
Population fragmentation compromises population viability, reduces a species ability to respond to climate change, and ultimately may reduce biodiversity. We studied the current state and potential causes of fragmentation in grizzly bears over approximately 1,000,000 km2 of western Canada, the northern United States (US), and southeast Alaska. We compiled much of our data from projects undertaken with a variety of research objectives including population estimation and trend, landscape fragmentation, habitat selection, vital rates, and response to human development. Our primary analytical techniques stemmed from genetic analysis of 3,134 bears, supplemented with radiotelemetry data from 792 bears. We used 15 locus microsatellite data coupled with measures of genetic distance, isolation-by-distance (IBD) analysis, analysis of covariance (ANCOVA), linear multiple regression, multi-factorial correspondence analysis (to identify population divisions or fractures with no a priori assumption of group membership), and population-assignment methods to detect individual migrants between immediately adjacent areas. These data corroborated observations of inter-area movements from our telemetry database. In northern areas, we found a spatial genetic pattern of IBD, although there was evidence of natural fragmentation from the rugged heavily glaciated coast mountains of British Columbia (BC) and the Yukon. These results contrasted with the spatial pattern of fragmentation in more southern parts of their distribution. Near the Canada–US border area, we found extensive fragmentation that corresponded to settled mountain valleys and major highways. Genetic distances across developed valleys were elevated relative to those across undeveloped valleys in central and northern BC. In disturbed areas, most inter-area movements detected were made by male bears, with few female migrants identified. North–south movements within mountain ranges (Mts) and across BC Highway 3 were more common than east–west movements across settled mountain valleys separating Mts. Our results suggest that relatively distinct subpopulations exist in this region, including the Cabinet, Selkirk South, and the decades-isolated Yellowstone populations. Current movement rates do not appear sufficient to consider the subpopulations we identify along the Canada–US border as 1 inter-breeding unit. Although we detected enough male movement to mediate gene flow, the current low rate of female movement detected among areas is insufficient to provide a demographic rescue effect between areas in the immediate future (0–15 yr). In Alberta, we found fragmentation corresponded to major east–west highways (Highways 3, 11, 16, and 43) and most inter-area movements were made by males. Gene flow and movement rates between Alberta and BC were highest across the Continental Divide south of Highway 1 and north of Highway 16. In the central region between Highways 1 and 11, we found evidence of natural fragmentation associated with the extensive glaciers and icefields along the Continental Divide. The discontinuities that we identified would form appropriate boundaries for management units. We related sex-specific movement rates between adjacent areas to several metrics of human use (highway traffic, settlement, and human-caused mortality) to understand the causes of fragmentation. This analysis used data from 1,508 bears sampled over a 161,500-km2 area in southeastern BC, western Alberta, northern Idaho, and northern Montana during 1979–2007. This area was bisected by numerous human transportation and settlement corridors of varying intensity and complexity. We used multiple linear regression and ANCOVA to document the responses of female and male bears to disturbance. Males and females both demonstrated reduced movement rates with increasing settlement and traffic. However, females reduced their movement rates dramatically when settlement increased to >20% of the fracture zone. At this same threshold, male movement declined more gradually, in response to increased traffic and further settlement. In highly settled areas (>50%), both sexes had a similar reduction in movements in response to traffic, settlement, and mortality. We documented several small bear populations with male-only immigration, highlighting the importance of investigating sex-specific movements. Without female connectivity, small populations are not viable over the long term. The persistence of this regional female fragmented metapopulation likely will require strategic connectivity management. We therefore recommend enhancing female connectivity among fractured areas by securing linkage-zone habitat appropriate for female dispersal, and ensuring current large source subpopulations remain intact. The fragmentation we documented may also affect other species with similar ecological characteristics: sparse densities, slow reproduction, short male-biased dispersal, and a susceptibility to human-caused mortality and habitat degradation. Therefore, regional inter-jurisdictional efforts to manage broad landscapes for inter-area movement will likely benefit a broad spectrum of species and natural processes, particularly in light of climate change. © 2011 The Wildlife Society.La fragmentación de la población compromete su viabilidad, reduce la capacidad de una especie a responder a los cambios climáticos y a la larga, puede llegar a reducir la biodiversidad. Hemos estudiado el estado actual de la fragmentación de los osos Grizzli y sus causas posibles en un territorio de 1.000.000 km2 que abarca el oeste de Canadá, el norte de los EE. UU. y el sureste de Alaska. Hemos compilado la mayor parte de la información a partir de proyectos emprendidos con varios fines incluyendo la estimación de las poblaciones y sus tendencias, la fragmentación de los paisajes, la selección del hábitat, los índices vitales y la respuesta al desarrollo humano. Nuestras técnicas primarias de análisis provienen de los análisis genéticos de 3134 osos, complementadas con datos de radio-telemetría de 792 osos. Utilizamos datos de marcadores de microsatélite en el locus 15 apareados con medidas de distancia genética, análisis de aislamiento por distancia, análisis de la covarianza (ANCOVA), regresión lineal múltiple, análisis de correspondencia multifactorial (para identificar divisiones en las poblaciones ó fragmentos sin asumir afiliación a un grupo) y métodos de asignación a fin de detectar los individuos migrantes entre áreas inmediatamente adyacentes. Estos datos corroboran observaciones de movimientos inter-áreas en nuestra base de datos de telemetría. En las áreas del norte se nota un patrón genético espacial de aislamiento por distancia aunque hay prueba de fragmentación natural por las montañas costeras escabrosas y los glaciares de Columbia Británica (BC) y del Yukon. Estos resultados contrastan con el patrón espacial de fragmentación de las partes más al sur y de su distribución. Cerca de la zona fronteriza Canadá-Estados Unidos, vemos una fragmentación extensiva que corresponde a los valles habitados y a las grandes autopistas. Se observaron distancias genéticas más elevadas en los valles desarrollados que en los valles naturales del centro y del norte de BC. En las áreas perturbadas, la mayoría de los movimientos inter-áreas los realizan los osos machos y se detectaron pocas hembras migrantes. Los movimientos norte-sur en las sierras y a través de la autopista 3 de BC fueron más comunes que los movimientos este-oeste en los valles habitados entre las sierras. Nuestros resultados sugieren la existencia de subpoblaciones relativamente distintas en esta región, incluyendo el Cabinet, Selkirk Sur y las poblaciones aisladas desde hace décadas de Yellowstone. Las tasas de movimiento actuales no parecen suficientes para considerar las subpoblaciones que identificamos a lo largo de la frontera Canadá-Estados Unidos como 1 unidad de entrecruzamiento. Aunque hemos detectado suficientes movimientos de machos para intervenir en el flujo de genes, la tasa actual de movimientos de hembras es insuficiente para proveer un efecto de rescate demográfico entre las áreas en el futuro inmediato (0-15 años). En Alberta, hemos encontrado una fragmentación que corresponde a las principales autopistas este-oeste (3, 11, 16 y 43) y la mayoría de los movimientos inter-áreas fueron realizados por machos. El flujo de genes y las tasas de movimientos entre BC y Alberta son más importantes en la línea divisoria continental al sur de la autopista 1 y al norte de la 16. En la región central entre las autopistas 1 y 11, hemos encontrado pruebas de fragmentación natural asociada con los glaciares y campos de nieve extensivos a lo largo de la línea divisoria continental. Las discontinuidades identificadas formarían límites apropiados para las unidades de gestión. Se han relacionado tasas de movimientos especificas a cada sexo entre áreas adyacentes con varias medidas de uso humano (tráfico en autopistas, poblados y mortalidad causada por humanos) para entender las causas de fragmentación. Este análisis contiene datos de 1508 osos cuyas pruebas fueron recopiladas en un área de 161.500 km2 que abarca el sureste de BC, el oeste de Alberta, el norte de Idaho y el norte de Montana del 1979 al 2007. En esta área se encuentran numerosos corredores de transporte y poblados humanos de intensidad y complexidad varias. Usamos la regresión lineal múltiple y ANCOVA para documentar las respuestas de hembras y machos a las perturbaciones. En ambos grupos se produjo una reducción de la tasa de movimientos ante el aumento de tráfico y poblados. Sin embargo, la tasa de movimiento de las hembras se vio reducida dramáticamente ante un aumento de poblado de más del 20% de la zona fragmentada. En este mismo punto la tasa de movimiento de los machos se redujo más gradualmente. En las zonas altamente pobladas (más del 50%) ambos sexos mostraron respuestas similares ante el tráfico, los poblados y la mortalidad. Se documentaron varias pequeñas poblaciones de osos con inmigración de machos solamente, lo que pone de manifiesto la importancia de examinar los movimientos específicos de cada sexo. Sin la conectividad de la hembra, las pequeñas poblaciones no son viables a largo plazo. La persistencia de esta meta-población fragmentada regional de hembras probablemente necesitará una gestión de conectividad estratégica. Por lo tanto, recomendamos acentuar la conectividad de hembras entre zonas fragmentadas para asegurar las conexiones entre zonas de hábitat apropiadas a la dispersión de hembras y asegurar la sobrevivencia de las grandes subpoblaciones originales actuales. La fragmentación aquí descrita puede también afectar otras especies de características similares: escasa densidad, reproducción lenta, la tendencia a la dispersión de los machos, susceptibilidad a mortalidad causada por humanos y degradación del hábitat. En consecuencia, un amplio espectro de especies y procesos naturales podrán beneficiar de los esfuerzos regionales interjurisdiccionales de gestión de paisajes de gran extensión para movimientos inter-áreas, particularmente ante los cambios climáticos.La fragmentation des populations compromet la viabilité des populations, réduit la capacité des espèces à s'adapter au changement climatique, pouvant ainsi réduire la biodiversité. Nous avons étudié l'état actuel et les causes potentielles de fragmentation chez les grizzlis sur environ 1 000 000 km2 incluant l'ouest du Canada, le nord des Etats-Unis, et le sud-est de l'Alaska. La majorité de nos données provient de projets conduits avec différents objectifs de recherche, incluant l'estimation de la taille et de l'évolution démographique des populations, la fragmentation du paysage, la sélection d'habitat, les taux vitaux, et les réponses au développement urbain. Nos principales techniques d'analyse étaient basées sur l'analyse génétique de 3 134 grizzlys, et complétées par des données radio télémétriques provenant de 792 ours. Nous avons utilisé des données provenant de 15 locus microsatellites, combinées avec des mesures de distance génétique, d'isolement par la distance, d'analyse de covariance (ANCOVA), de régression linéaire multiple, d'analyse multifactorielle par correspondance (pour identifier les divisions de populations sans supposition préalable sur l'appartenance de chaque individu à un groupe), et avec des méthodes déterminant l'appartenance à une population pour détecter les individus migrant entre zones directement adjacentes. Ces données ont corroboré des observations de mouvements d'ours entre zones provenant de notre base de données télémétriques. Dans les zones du nord, nous avons trouvé un effet spatial d'isolement génétique par la distance, bien qu'il y avait des signes de fragmentation naturelle due aux chaînes côtières englacées de Colombie Britannique (BC) et du Yukon. Ces résultats contrastent avec les effets de fragmentation observés dans les zones plus au sud. Près de la frontière Canada-Etats-Unis, nous avons trouvé une fragmentation élevée correspondant aux vallées montagneuses développées et aux autoroutes principales. Les distances génétiques entre vallées développées étaient élevées en comparaison avec celles observées entre vallées non-développées dans le centre et le nord de la Colombie Britannique. Entre les zones perturbées, la majorité des mouvements étaient effectués par les ours mâles, tandis que peu de femelles en dispersion étaient identifiées. Les mouvements nord-sud au sein des chaînes de montagnes et traversant l'autoroute 3 de Colombie Britannique étaient plus fréquents que les mouvements est-ouest effectués entre les vallées développées séparant ces zones montagneuses. Nos résultats suggèrent que des sous-populations plutôt distinctes existent dans cette région, incluant le Cabinet, Selkirk South, et les populations du Yellowstone isolées depuis plusieurs décennies. Les taux de mouvements actuels ne semblent pas suffisants pour considérer les sous-populations identifiées le long de la frontière Canada-Etats-Unis comme une unité de reproduction. Malgré le fait que nous avons détecté assez de mouvements de la part des mâles pour favoriser le flux de gènes, le faible taux de mouvements effectué par les femelles est insuffisant pour fournir un effet de renforcement démographique entre zones dans un futur immédiat (0-15 ans). En Alberta, nous avons trouvé que la fragmentation correspondait aux autoroutes est/ouest principales (autoroutes 3, 11, 16, et 43) et que la plupart des mouvements entre zones étaient réalisés par les mâles. Les taux de flux génétique et de mouvements entre l'Alberta et la Colombie Britannique étaient les plus élevés à travers la ligne de partage des eaux continentales (Continental Divide) au sud de l'autoroute 1 et au nord de l'autoroute 16. Dans la région centrale entre les autoroutes 1 et 11, nous avons détecté des signes de fragmentation naturelle associés aux larges glaciers et aux champs de glace situés le long du Continental Divide. Les discontinuités que nous avons identifiées forment des limites appropriées pour la création d'unités de gestion. Nous avons lié les taux de mouvements de chaque sexe entre zones adjacentes à plusieurs mesures d'activité humaine (trafic autoroutier, développement, mortalité due à l'homme) pour comprendre les causes de la fragmentation. Cette analyse a utilisé des données de 1508 ours obtenues sur une surface de 161 500 km2 incluant le sud-est de la Colombie Britannique, l'ouest de l'Alberta, le nord de l'Idaho, et le nord du Montana entre 1979 et 2007. Cette surface était segmentée par de nombreuses infrastructures de transport, et par des corridors de développement d'intensité et de complexité variées. Nous avons utilisé des régressions linéaires multiples et des ANCOVA pour documenter les réponses des ours femelles et mâles aux perturbations. Les mâles ainsi que les femelles ont montré une réduction du taux de mouvements avec l'augmentation du développement et du trafic. Cependant, les femelles réduisait leurs mouvements très fortement quand le taux de développement était supérieur à 20% autour la zone autoroutière. A ce même seuil, les mouvements des mâles déclinaient de manière plus graduelle en réponse à l'augmentation du trafic routier et du développement. Dans les zones les plus développées (>50%), les 2 sexes avaient une diminution similaire du taux de mouvements en réponse au trafic, au développement, et à la mortalité. Nous avons documenté plusieurs petites populations d'ours avec une immigration faite uniquement par les mâles, soulignant l'importance de l'étude des mouvements de chaque sexe. Sans connectivité entre les femelles, les petites populations ne sont pas viables à long terme. La maintenance de cette métapopulation régionale fragmentée, due à l'absence de mouvements des femelles, va sûrement demander une gestion stratégique de la connectivité. Nous recommandons donc d'améliorer la connectivité des femelles en sécurisant des surfaces d'habitat “lien” appropriées pour faciliter leur dispersion entre les zones fragmentées, et d'assurer que les grandes sous-populations sources restent intactes. La fragmentation que nous avons documentée peut aussi affecter d'autres espèces ayant des caractéristiques écologiques similaires: faibles densités, reproduction lente, dispersion des mâles sur de courtes distances, et sensibilité à la mortalité due à l'homme ainsi qu'à la dégradation de l'habitat. Donc, des efforts régionaux entre juridictions pour gérer de larges paysages pour faciliter les mouvements entre zones vont probablement bénéficier un large spectre d'espèces et de processus naturels, en particulier en vue du changement climatique.
We studied a desert bighorn sheep (Ovis canadensis) population in the Mazatzal Mountains (primary study area) in central Arizona and population indices on reference areas between 1989 and 2003. We evaluated disease exposure and nutritional status of desert bighorn sheep, vegetation parameters, predator diets, and mountain lion (Puma concolor) harvest and abundance (1999–2003) and mountain lion predation (1995–2003) as factors potentially affecting desert bighorn sheep and population parameters. We measured rainfall monthly, monitored demography and relative abundance of desert bighorn sheep using aerial surveys, captured and placed radio collars on desert bighorn sheep, and collected samples of blood, parasites, and other pathogenic agents from captured animals. We measured mineral content, relative use, and structural composition of vegetation and determined diets of desert bighorn sheep adults and lambs, dietary intakes of nitrogen (FN), 2,6-diaminopimelic acid (FDAPA), neutral detergent fiber, and minerals using fecal analyses. We incorporated mountain lion reductions as an experimental element, monitored harvest, and used track surveys as an index of relative abundance of the predator and monitored radio-collared desert bighorn sheep to determine mortalities and causes of death. We determined diets of bobcats (Lynx rufus), coyotes (Canis latrans), and mountain lions using fecal analyses. Drought conditions occurred during summer (July-September) and winter (November-April) during 4 and 3 years, respectively, between 1999 and 2003. Annual surveys indicated that the Mazatzal Mountains population declined during drought between 1994 and 1997, experienced low growth and lamb production coincident with above-normal rainfall in 1998 and drought in 1999, and exhibited higher growth, production, and productivity during 2000–2003 despite persistent drought conditions during this period. We observed no clinical symptoms of disease in radio-collared desert bighorn sheep, and hematological and other evidence of exposure to disease agents was unremarkable. Population indices on the primary study and reference areas were positively correlated with winter (November-April) rainfall. We found no evidence of forage overutilization on the primary study area. Rainfall on Mazatzal Mountains was associated with differences in primary production, particularly of forbs, forage mineral concentrations, and diets, nutritional status, and demographic attributes of desert bighorn sheep between 1999 and 2003. Higher winter rainfall was associated with higher forb growth, and higher rainfall was associated with higher concentrations of P and Se but lower levels of Fe in browse; higher concentrations of Ca, P, and Zn in forbs; and higher levels of P, Se, and Zn in grasses. Narrower mean Ca:P ratios of browse and forbs were associated with higher rainfall. Diets of desert bighorn sheep adults and lambs generally were similar, particularly near summer, and forbs tended to predominate in diets during wetter and drier years. Higher winter rainfall was associated in adult feces with more prolonged winter-to-spring increases in FN and FDAPA concentrations, higher fecal phosphorus, lower fecal Ca levels, and narrower fecal Ca:P and Na:K ratios, but levels of fecal Na increased during the driest year. Higher winter rainfall corresponded in lamb feces with higher levels of FN, FDAPA, and fecal P; lower concentrations of fecal Ca; and narrower fecal Ca:P ratios. Thus, we hypothesized that diets and nutritional status of desert bighorn sheep adults and lambs tended to correspond with rainfall patterns and associated differences in relative abundance and mineral content of forages. We found no evidence that bobcats or coyotes preyed on or scavenged desert bighorn sheep. Decline of desert bighorn sheep abundance during 1994–1997 was greater than declines on reference areas lacking mountain lions despite continually higher, and a lesser decline in, winter rainfall on the primary study area. In comparison, population indices on a reference area and on Mazatzal Mountains increased between 1999 and 2003 in association with predator reductions and lower abundance of mountain lions and predation of radio-collared animals despite continued occurrences of drought during this period. We thus identified 2 proximate factors that likely acted to influence demographic trends of the Mazatzal Mountains desert bighorn sheep population: nutritional status (higher rainfall [ultimate factor] was associated with higher availability and differences in mineral content of forages and improved indices of desert bighorn sheep nutritional status) and predation by mountain lions. We hypothesize that nutritional status and mountain lion predation during a period of drought influenced desert bighorn sheep population parameters in Mazatzal Mountains and that short-term removal of mountain lions by lethal harvest contributed to higher growth and productivity of the small, isolated population, even during periods of drought.RESUMENEstudiamos una población de borregos cimarrones (Ovis Canadensis) del desierto en las montañias de Mazatzal (área primaria del estudio), zona central de Arizona, así como índices poblacionales en las áreas de referencia entre 1989 y 2003. Evaluamos la susceptibilidad a enfermedades y el estado alimenticio de los borregos cimarrones del desierto, los parámetros de la vegetación, las dietas de los depredadores y el aprovechamiento y abundancia del puma (Puma concolor) (1999–2003) y la depredación del puma (1995–2003) como factores que potencialmente afectaban a los borregos cimarrones del desierto y a los parámetros de población. Medimos las precipitaciones mensuales de lluvia, monitoreamos la demografía y la abundancia relativa de los borregos cimarrones del desierto empleando estudios aéreos, capturamos y colocamos radiocollares en los borregos cimarrones del desierto y recolectamos muestras de sangre, parásitos y otros agentes patógenos de los animales capturados. Medimos las substancias minerales, el uso relativo y la composición estructural de la vegetación y, por medio de análisis fecales, determinamos las dietas de los borregos cimarrones del desierto, tanto en adultos como en corderos, las ingestiones dietéticas de nitrógeno (FN), 2, el ácido 6-diaminopimélico (FDAPA), fibra de detergente neutral y minerales. Incorporamos, como elemento experimental, una reducción en los pumas, monitoreamos el aprovechamiento y utilizamos estudios de trayectoria como índice de la abundancia relativa del depredador y monitoreamos los radiocollares de los borregos cimarrones para determinar las mortalidades y las causas de muerte. Determinamos las dietas de gatos monteses, coyotes y pumas por medio de análisis de materia fecal. Se produjeron situaciones de sequía durante el verano (julio a septiembre) y el invierno (noviembre a abril), durante 4 y 3 años, respectivamente, entre 1999 y 2003. Los estudios anuales indicaron que la población de las montañas de Mazatzal declinó durante la época de sequía entre 1994 y 1997, el bajo crecimiento experimentado y la producción de corderos coinciden con la precipitación normal antedicha en 1998 y la sequía en 1999 y presentaron un crecimiento, una producción y una productividad más altos durante 2000–2003 a pesar de las condiciones persistentes de sequía durante este período. No observamos ningún síntoma clínico de enfermedad en los borregos cimarrones del desierto con radiocollar y la evidencia hematológica y la procedente de otras exposiciones a agentes de enfermedad no fue fuera de lo común. Los índices de población en las áreas primarias del estudio y de la referencia fueron correlacionados positivamente con las precipitaciones de invierno (noviembre a abril). No encontramos ninguna evidencia de utilización excesiva de forraje en el área primaria del estudio. La precipitación en las montañas de Mazatzal fue asociada a diferencias en la producción primaria particularmente de hierbas, de concentraciones minerales del forraje y de dietas, del estado alimenticio y de cualidades demográficas de los borregos cimarrones del desierto entre 1999 y 2003. Una precipitación más elevada durante el invierno se asoció a un crecimiento más alto de hierbas y una precipitación más alta se asoció a concentraciones más altas de P y Se pero a niveles más bajos de Fe en el ramón, concentraciones más altas de Ca, P, y Zn en hierbas y niveles más altos de P, Se y Zn en pastos. Un promedio más restringido de cantidades de Ca:P en ramones y otras hierbas fue relacionado con precipitaciones más elevadas. Las dietas de adultos y corderos de los borregos cimarrones del desierto eran generalmente similares, particularmente cerca del verano y las hierbas tenían tendencia a predominar en las dietas tanto durante los años de más precipitaciones como durante los más secos. Las precipitaciones más elevadas del invierno fueron asociadas a heces en los adultos con un mayor aumento en las concentraciones de FN y de FDAPA prolongados en invierno y primavera, fósforo fecal más alto, niveles de CA más bajos en la materia fecal y cocientes fecales más limitados de Ca:P y de Na:K, pero los niveles de Na fecal aumentaron durante el año más seco. Las precipitaciones más elevadas del invierno correspondieron con que las heces del cordero contenían niveles más altos de FN, de FDAPA, y de P fecal, concentraciones más bajas de CA fecal y cocientes fecales más limitados de Ca:P. En consecuencia, presumimos que las dietas y el estado alimenticio de adultos y corderos de los borregos cimarrones del desierto tienden a corresponder con los patrones de precipitación y diferencias asociadas en abundancia relativa y al contenido mineral de forrajes. No encontramos ninguna evidencia de que los gatos monteses (Lynx rufus) o los coyotes (Canis latrans) cazaran borregos cimarrones del desierto o se alimentaran de ellos. La disminución de la abundancia de los borregos cimarrones del desierto durante 1994–1997 fue mayor que las disminuciones en las áreas de referencia que carecían de pumas, a pesar de una cantidad mayor continuada, y de una disminución reducida, en las precipitaciones de invierno en el área primaria del estudio. En comparación, los índices de la población en el área de referencia y en las montañas de Mazatzal aumentaron entre 1999 y 2003 en conexión con las reducciones de depredadores y una menor abundancia de pumas y la depredación de animales con radiocollares, a pesar de que durante este período continuaron las sequías. Identificamos así 2 factores relacionados que probablemente han influenciado las tendencias demográficas de la población de los borregos cimarrones de las montañas de Mazatzal: el estado alimenticio (precipitaciones más elevadas [último factor] fueron asociadas a una disponibilidad y a diferencias más altas en el contenido de minerales en el forraje y mejoraron los índices del estado alimenticio de los borregos cimarrones del desierto) y la depredación de los pumas. Presumimos que el estado nutricional y la depredación del puma durante el período de sequía influyó sobre los parámetros de la población de los borregos cimarrones del desierto en las montañas de Mazatzal, y el retiro a corto plazo de los pumas, cuyo aprovechamiento es letal, contribuyó a un crecimiento y a una productividad más altos de la pequeña y aislada comunidad, incluso durante períodos de sequía.Evaluation des Facteurs Influant Éventuellement Sur Une Population de Mouflons D'amérique du DésertRÉSUMÉNous avons étudié une population de mouflons d'Amérique du désert (Ovis canadensis) dans les montagnes Mazatzal (principale zone d'étude), au centre de l'Arizona, et les indices des populations dans les zones de référence de 1989 à 2003. Nous avons évalué l'exposition à la maladie et l'état nutritionnel des mouflons d'Amérique du désert, les paramètres de la végétation, le régime alimentaire des prédateurs, la prise et l'abondance du couguar (Puma concolor) (de 1999 à 2003) et la prédation par les couguars (de 1995 à 2003) comme facteurs susceptibles de toucher le mouflon d'Amérique du désert et les paramètres de la population. Nous avons mesuré les précipitations de façon mensuelle, surveillé la démographie et l'abondance relative du mouflon d'Amérique du désert à l'aide de relevés aériens en plus de capturer des individus et de leur placer des colliers émetteurs. De plus, nous avons recueilli des échantillons de sang, des parasites et d'autres agents pathogènes sur les individus capturés. Nous avons mesuré la teneur en minéraux, l'utilisation relative et la composition structurale de la végétation, puis déterminé le régime alimentaire du mouflon d'Amérique du désert adulte et juvénile, les apports alimentaires en azote (FN), en 2, en acide diaminopimélique 6 (FDAPA), en cellulose au détergent neutre et en minéraux à l'aide d'analyses fécales. Nous avons incorporé la diminution du nombre de couguars à titre d'élément expérimental, surveillé les prises et utilisé des relevés des pistes en tant qu'indice de l'abondance relative du prédateur, puis surveillé les mouflons d'Amérique du désert munis d'un collier émetteur pour déterminer les mortalités et les causes du décès. Nous avons déterminé le régime alimentaire des lynx roux, des coyotes et des couguars à l'aide des analyses fécales. Des conditions de sécheresse ont prévalu au cours de l'été (de juillet à septembre) et de l'hiver (de novembre à avril) pendant 4 et 3 ans, respectivement, de 1999 à 2003. Les relevés annuels ont indiqué que la population des montagnes Mazatzal a subi un déclin lors de la sécheresse entre 1994 et 1997, connu une faible croissance et une faible production de petits qui ont coïncidé avec des précipitations au dessus de la moyenne en 1998 et la sécheresse en 1999, puis montré une croissance, une production et une productivité accrues de 2000 à 2003 malgré la sécheresse persistante au cours de cette période. Nous n'avons observé aucun symptôme clinique de maladie chez les mouflons d'Amérique du désert munis d'un collier émetteur, et aucune preuve hématologique ou autre d'exposition à des maladies n'a été remarquée. Les indices de population dans la principale zone d'étude et la zone de référence ont été mis en corrélation de façon positive avec les précipitations connues en hiver (de novembre à avril). Nous n'avons trouvé aucune preuve de surpâturage dans la principale zone d'étude. Les précipitations dans les montagnes Mazatzal ont été associées aux différences de production primaire, particulièrement de latifoliés, aux concentrations de minéraux du pâturage ainsi qu'aux régimes alimentaires, aux états nutritionnels et aux attributs démographiques du mouflon d'Amérique du désert de 1999 à 2003. Les précipitations plus importantes de l'hiver ont été associées avec une croissance accrue de latifoliés et ces précipitations plus importantes ont été associées avec de plus grandes concentrations de P et de Se, mais avec un niveau moindre de Fe dans le pâturage, des concentrations plus élevées de Ca, de P, et de Zn dans les latifoliés ainsi que des niveaux accrus de P, de Se et de Zn dans les graminées. Le rapport moyen plus étroit entre le Ca et le P du pâturage et des latifoliés a été associé aux précipitations plus importantes. Le régime alimentaire du mouflon d'Amérique du désert, tant adulte que juvénile, est généralement très semblable, particulièrement à l'approche de l'été, et les latifoliés ont eu tendance à être prédominants dans les régimes au cours des années plus humides et plus sèches. Les précipitations plus importantes de l'hiver ont été associées, dans les matières fécales des adultes, à une augmentation plus prolongée en hiver et au printemps des concentrations de FN et de FDAPA, à davantage de phosphore fécal, à des niveaux moindres de Ca fécal ainsi qu'à des rapports entre le Ca et le P et le Na et le K fécaux plus étroits. Cependant, les niveaux de Na fécal ont augmenté lors de l'année la plus sèche. Les précipitations élevées connues en hiver se sont traduites, dans les matières fécales des petits, par des niveaux accrus de FN, de FDAPA et de P fécal, des concentrations moindres de Ca fécal et un rapport entre le Ca et le P fécal plus étroit. Par conséquent, nous avons émis l'hypothèse que les régimes alimentaires et les états nutritionnels du mouflon d'Amérique du désert, tant adulte que juvénile, avaient tendance à correspondre au modèle des précipitations et aux différences connexes de l'abondance relative et de la teneur en minéraux des pâturages. Nous n'avons trouvé aucune preuve selon laquelle les couguars (Lynx rufus) ou les coyotes (Canis latrans) avaient pris le mouflon d'Amérique du désert comme proie ou s'étaient nourris de leurs carcasses. Le déclin de l'abondance de mouflons d'Amérique du désert connu de 1994 à 1997 a été plus importante que les déclins connus dans les zones de référence où on ne trouvait pas de couguars, malgré les précipitations hivernales toujours croissantes et une baisse moins importante de celles-ci dans la principale zone d'étude. Par comparaison, les indices de population dans une zone de référence et dans les montagnes Mazatzal ont connu une augmentation de 1999 à 2003 de concert avec la réduction des prédateurs, de l'abondance de couguars et de la prédation des animaux munis d'un collier émetteur, malgré l'occurrence continue de la sécheresse au cours de cette période. Nous avons donc déterminé deux facteurs immédiats susceptibles d'avoir influer sur les tendances démographiques de la population de mouflons d'Amérique du désert des montagnes Mazatzal: l'état nutritionnel (les précipitations accrues [principal facteur] ont été associées à une plus grande disponibilité et aux différences de teneur en minéraux des pâturages ainsi qu'aux indices améliorés de l'état nutritionnel du mouflon d'Amérique du désert) et la prédation par les couguars. Nous avons formulé l'hypothèse que les états nutritionnels et la prédation par les couguar au cours d'une période de sécheresse ont influé sur les paramètres de population du mouflon d'Amérique du désert dans les montagnes Mazatzal, et que la suppression à court terme des couguars par la prise a contribué à une croissance plus importante et é la productivité de la population, qui est petite et isolée, même au cours de périodes de sécheresse.
In arid regions of the southwestern United States, water is often considered a primary factor limiting distribution and productivity of desert ungulates, including desert bighorn sheep (Ovis canadensis mexicana). Thus, wildlife management agencies and sportsmen's organizations have invested substantial time and resources in the construction and maintenance of water catchments. Although the availability of freestanding water sources is believed to influence many aspects of the ecology of desert bighorn sheep, the efficacy of these water sources has been questioned and has not been examined experimentally. We used a before-after-control-impact study design to determine if removal of water catchments changed diet, characteristics of foraging areas used by female desert bighorn sheep, home-range size, movement rates, distance to catchments, adult mortality, productivity, or juvenile recruitment in 2 mountain ranges on the Cabeza Prieta National Wildlife Refuge, Arizona, USA. During pretreatment (2002–2003), we ensured that water catchments were available to desert bighorn sheep in both mountain ranges; during posttreatment (2004–2005), we drained all water catchments in the treatment range. We measured diet composition, characteristics of foraging areas, 50% and 95% kernel home ranges, movement rates, and distance to water catchments seasonally from 2002 to 2005. We also estimated adult survival, lamb:female, and yearling:female ratios from 2002 to 2005. We predicted that removal of water catchments would result in 1) increased use of foraging areas with more vegetation cover, more thermal cover, and higher succulent abundance; 2) increased consumption of cacti and other succulents; 3) an increase in home-range size, movement rates, and distance to nearest catchment; and 4) a decrease in adult survival, productivity, and juvenile recruitment. Removal of water catchments in the treatment range did not result in predicted changes in diet, foraging area selection, home-range size, movement rates, mortality, productivity, or recruitment. Female desert bighorn sheep did use areas with more thermal cover during the summer after removal of water catchments, but other characteristics of foraging areas used by bighorn sheep and their diet did not change appreciably with removal of water catchments. We did not document changes in home-range area, movement rates, or distance sheep were from water during hotter months; we only documented changes in home-range area, movement rates, and distance to water catchments during winter and autumn. There were 10 desert bighorn sheep mortalities in the treatment range and 8 in the control range; 7 mortalities in each mountain range were during pretreatment. Twelve of the 18 total mortalities occurred during summer. Survival rate was lower during pretreatment than posttreatment in both mountain ranges. We did not document increased mortality or a change in lamb:female or yearling:female ratios after removal of water catchments. Home-range area and movement rates declined with increasing precipitation. Annual survival rates increased with increases in the current year's total precipitation and total precipitation during the previous year; annual survival rates declined with increases in average daily temperature during winter. There was a severe drought during pretreatment and abnormally wet conditions during posttreatment. The increase in precipitation that coincided with removal of water sources improved forage conditions during posttreatment and may have provided adequate water for female desert bighorn sheep. The lack of change in home-range size, movement rates, and distance to the nearest water catchment during hot, dry seasons after removal of water sources suggests that forage conditions played a greater role in determining home-range area and movement rates than did the presence of water catchments. Higher mortality rates during the drought of the pretreatment period indicates that during droughts as severe as that of 2002, presence of water catchments was not sufficient to prevent mortalities of desert bighorn sheep and a lack of forage quality and quantity was likely the primary limiting factor of the population during this time. Improving forage conditions during posttreatment, increases in forage moisture content, and availability of naturally occurring sources of free water in the treatment range likely minimized any impact of removing water catchments on survival rates and lamb:female and yearling:female ratios. However, due to the climatic conditions during the study we were unable to assess how the treatment population would have responded to a lack of water sources during a drought period. The influence of anthropogenic water catchments, if any, on desert bighorn sheep populations may be strongest during years with weather conditions that are neither drought nor wet periods. Given the high interannual variability in precipitation in many areas of the arid Southwest, it is important for wildlife managers to determine if and when water is the primary limiting factor for populations of desert bighorn sheep in order to make the most efficient use of agency time and resources.RESEMENEn regiones áridas del suroeste de Estados Unidos, agua es a menudo considerada el primer factor limitante en la distribución y productividad de ungulados, incluyendo el borrego cimarrón del desierto (Ovis canadensis mexicana). Por lo tanto, las agencias de manejo de vida silvestre y organizaciones de deportes han invertido mucho tiempo y recursos en la construcción y mantenimiento de sistemas de captura de agua. A pesar que la disposición de fuentes de agua libre se cree que influencia muchos aspectos de la ecología del borrego cimarrón del desierto, la eficacia de estas fuentes de agua ha sido cuestionada y no ha sido evaluada experimentalmente. Nosotros usamos un estudio denominado control-de-impacto-antes-y-después diseñado para determinar si la remoción de sistemas de captura de agua generan un cambio en el régimen alimenticio, características de las áreas usadas para el forraje por hembras, y el rango de movimiento local, tasas de movimiento, distancia a los sistemas de captura de agua, mortalidad adulta, productividad, y reclutamiento juvenil en dos rangos de montaña en el Refugio de Vida Silvestre Nacional Cabeza Prieta, Arizona. Durante el periodo de pre-tratamiento (2002–2003) nos aseguramos que los sistemas de captura de agua estuvieran disponibles a todos los borregos cimarrón en ambos rangos montañosos; durante el periodo de postratamiento nosotros vaciamos todos los sistemas de captura de agua en el rango de tratamiento. Nosotros medimos la composición dietética, características forrajeras en el área, 50% y 95% kernel de rango local, tasas de movimiento, y las distancias a los sistemas de agua de captura temporalmente desde el 2002 al 2005. También estimamos la sobrevivencia de los adultos, y la relación de las hembras con una año cumplido del 2002 al 2005. Nosotros predijimos que la remoción de sistemas de captura de agua resultaría en lo siguiente: 1) incrementa el uso de aras de forraje con mas cobertura vegetal, mas protección a las temperaturas, y mayor abundancia de suculentas; 2) incremento en consumo de cactáceas y otras suculentas; 3) un incremento en el rango de movimiento local, tasas de movimiento, distancia al sistemas de captura de agua más cercano; 4) un decrecimiento en la tasa de sobrevivencia adulta, productividad y reclutamiento juvenil. La remoción de los sistemas de captura de agua en el rango de tratamiento no resulto en la predicción de cambios de composición dietética, selección de áreas de forraje, tamaño del rango local, tasas de movimiento, mortalidad, productividad o reclutamiento. La hembras de borregos cimarrón usaron áreas de mayor cobertura sombreada durante los meses del verano después de remover los sistemas de captura de agua, pero otras características de áreas de forraje usadas por los borregos cimarrones y su dieta no cambio apreciablemente con la remoción de estos sistemas. No documentamos cambios en el incremento del tamaño del rango de movimiento local, tasas de movimiento, o distancia convencional donde se encuentra agua en meses de verano; cambios en el rango local, tasas de movimiento, y distancias a los sistemas de captura de agua fueron documentados solo durante las temporadas de otoño e invierno. Se encontraron 10 mortalidades de borrego cimarrón en el rango de tratamiento y 8 en el rango control; 7 mortalidades en cada rango montañoso donde durante el periodo de pretratamiento. Doce de dieciocho mortalidades ocurrieron durante el verano. Las tasas de movimiento fueron más bajas durante el periodo de pre-tratamiento que durante el pos-tratamiento en ambos rango de montaña. No documentamos incrementos en mortalidad o cambio en los rango de relación borrego: hembra o hembras que han cumplido un ano después de haber removido los sistemas de captura de agua. El rango del area local y tasas de movimiento declinaron con la precipitación. Las tasas de sobrevivencia anual se incrementaron con el incremento en la precipitación total al ano y la precipitación total del año previo; las tasa de sobrevivencia declinaron con el incremento de la temperatura promedio diaria durante el invierno. Se presentaron varias sequias durante el periodo de pretratamiento y las condiciones anormalmente húmedas durante el periodo de post-tratamiento pudo proveer agua adecuada para las hembras del borrego cimarrón. Después de remover las fuentes de agua no observamos cambio en el tamaño del rango local, en las tasas de movimiento, y en la distancia al sistema de captura de agua más cercano durante la temporada caliente y seca; esto sugiere que las condiciones del forraje jugó un rol mas importante en determinar el área de rango local y tasas de movimiento que la presencia de sistemas de captura de agua. Las tasas de mortalidad más altas durante la sequia del periodo de pretratamiento indica que durante las sequias tan severas como la del 2002, la presencia de sistemas de captura de agua no fue suficiente para prevenir la mortalidad del borrego cimarrón y la carencia de forraje de calidad y cantidad fue el principal factor limitante de la población durante este periodo. Condiciones de forraje mejoradas durante el periodo de pos-tratamiento, incremento el contenido de humedad del forraje, y la disposición de fuentes de agua libre que ocurren naturalmente en el rango de tratamiento posiblemente minimizo cualquier impacto relacionado con la remoción de las fuentes de agua en las tasas de sobrevivencia y la relación borrego: hembra y el rango de hembras de un año o mas:hembras. Sin hembra, debido a las condiciones climáticas durante el estudio nos fue difícil evaluar como la población tratada hubiera respondido a la carencia de fuentes de agua durante un periodo de sequia. La influencia de sistemas de captura de agua antropogénicos, si los hay, en la población de borrego cimarrón podría ser mas fuerte durante condiciones mas húmedas que en sequías o en periodos húmedos. Dado la alta variabilidad interannual en la precipitación en muchas áreas del sudoeste árido, es importante que los encargados de la fauna se determinen si y cuando el agua es el factor limitador primario para las poblaciones de borrego cimarrón del desierto para hacer el uso más eficiente de tiempo y de recursos de la agencia.RÉSUMÉDans les régions arides du sud-ouest des États-Unis, l'eau est souvent considérée comme un facteur primaire limitant la distribution et la productivité des ongulés du desert, y compris les mouflons dAmérique du desert (Ovis canadensis mexicana). Ainsi, les agences de gestion de la faune et les organisations sportives ont investi beaucoup de temps et de ressources dans la construction et la maintenance de bassins de captage d'eau. Bien que l'accessibilité à des sources d'eau naturelles soit considérée influencer plusieurs aspects de l'écologie du mouflon dAmérique du desert, l'efficacité de ces sources d'eau a été mise en question et n'a pas été examinée expérimentalement. Nous utilisons un principe d'étude BACI (before-after-control-impact: contrǒle des impacts par comparaison avec l'état initial) pour déterminer si la suppression des bassins d'eau change l'alimentation, les caractéristiques des régions de quěte alimentaire utilisées par les mouflons dAmérique du desert femelles, la dimension du domaine vital, les taux de mouvement, la distance jusqu'aux bassins, la mortalité des adultes, la productivité, ou le recrutement des jeunes dans 2 chaǐnes de montagnes du Cabeza Prieta National Wildlife Refuge en Arizona. Durant la période de prétraitement (2002–2003), nous nous sommes assuré que les bassins de captage d'eau soient disponibles aux mouflons dAmérique du désert dans les deux chaǐnes de montagnes; durant la période de post-traitement (2004–2005), nous avons drainé tous les bassins d'eau dans la zone de traitement. Nous avons mesuré la composition alimentaire, les caractéristiques des régions de quěte alimentaire, les 50% et 95% du centre de l'aire vitale, les taux de mouvement, et la distance jusqu'aux bassins de captage d'une façon saisonnière entre 2002 et 2005. Nous avons aussi estimé la survie des adultes, etles rapports agneau:femelle et animaux de 1 an:femelle entre 2002 et 2005. Nous avons prédit que la suppression des bassins de captage d'eau résulterait en: 1) une utilisation plus prononcée des régions de quěte alimentaire contenant plus de couverture végétale, plus de couverture thermique, et présentant une abondance de plantes grasses (succulentes) plus élevée; 2) une consommation plus élevée de cactus et autres succulentes; 3) une augmentation de la taille du domaine vital, des taux de mouvement, de la distance jusqu'au bassin le plus proche; 4) une diminution de la survie des adultes, de la productivité et du recrutement des jeunes. La suppression des bassins de captage d'eau dans la zone de traitement n'a pas engendré les modifications prédites en ce qui concerne l'alimentation, la selection de la région de recherche alimentaire, la taille de l'aire vitale, les taux de mouvement, la mortalité, la productivité ou le recrutement. Les mouflons dAmérique du désert femelles ont utilisé des régions avec une couverture thermique plus importante durant les mois d'été après la suppression des bassins d'eau, mais les autres caractéristiques liées aux régions de quěte alimentaire utilisées par les mouflons dAmérique du désert ainsi que leur alimentation n'ont pas changé d'une façon remarquable suite à la suppression des bassins de captage. Nous n'avons pas observé de changements liés à la taille de l'aire vitale, aux taux de mouvement, ou à la distance des mouflons aux points d'eau durant les mois les plus chauds; nous avons seulement observés des changements liés à la taille de l'aire vitale, aux taux de mouvement, et à la distance jusqu'aux bassins de captage durant les saisons d'hiver et d'automne. Il y a eu 10 mortalités du mouflons d'Amérique dans la zone de traitement et 8 dans la zone de contrǒle; il y a eu 7 mortalités dans chaque chaǐne de montagne durant la période de prétraitement. Douze des 18 mortalités totales se sont produites durant l'été. Dans les deux chaǐnes montagneuses, le taux de survie était plus bas durant le prétraitement en comparaison avec la période de post-traitement. Nous n'avons pas observé une augmentation de la mortalité ou un changement dans les rapports agneau:femelle et animaux de 1 an:femelle après la suppression des bassins de captage d'eau. L'aire du domaine vital et les taux de mouvement ont diminué avec l'augmentation des précipitations. Les taux de survie annuels ont augmenté avec l'augmentation des précipitations totales de l'année en cours ainsi que les précipitations totales de l'année précédente; les taux de survie annuels ont diminué avec les augmentations de la température journalière moyenne durant l'hiver. Il y a eu une sécheresse prononcée durant la période de prétraitement ainsi que des conditions inhabituellement humides durant la période de post-traitement. L'augmentation des précipitations qui a coïncidé avec la suppression des sources d'eau a amélioré les conditions de quěte alimentaire durant la période de post-traitement et a peut-ětre pu fournir une source d'eau adéquate pour les mouflons d'Amérique femelles. L'absence de modification de l'aire vitale, des taux de mouvement, et de la distance au bassin de captage d'eau le plus proche durant les saisons chaudes et sèches après la suppression des sources d'eau suggère que les conditions de recherche alimentaire ont eu une influence plus importante sur l'aire du domaine vital et sur les taux de mouvement que la présence ou l'absence de bassins d'eau. Les taux de mortalité plus élevés durant la sécheresse de la période de prétraitement indiquent que durant des sécheresses aussi graves que celle de 2002, la présence de bassins de captage n'était pas suffisante pour éviter les mortalités du mouflon d'Amérique du désert, et il est probable qu'une diminution de la qualité et de la quantité de la recherche alimentaire soit le facteur limitant principal de la population durant cette période. Il est probable que l'amélioration des conditions de quěte alimentaire durant la période de post-traitement, l'augmentation du contenu humide lors de la recherche de nourriture, ainsi que la disponibilité de sources naturelles d'eau libre dans la zone de traitement aient minimisé les impacts de la suppression des bassins d'eau sur les taux de survie et sur les rapports agneau:femelle et animaux de 1 an:femelle. Cependant, à cause des conditions climatiques durant l'étude, il nous était impossible d'estimer de quelle manière la population de traitement aurait répondu à un manque de source d'eau durant une période de sécheresse. Il est possible que l'influence des bassins de captage anthropiques, s'ils sont présents, sur les populations de mouflons d'Amérique du désert soit maximale durant les années présentant des conditions météorologiques n'étant des périodes ni de sécheresse ni humides. Etant donné la variabilité interannual élevée dans la précipitation dans beaucoup de secteurs du sud-ouest aride, il est important que les directeurs de faune déterminent si et quand l'eau est le facteur limiteur primaire aux populations des mouflons d'Amérique du désert afin de faire l'utilisation la plus efficace du temps et des ressources d'agence.
ABSTRACT  We conducted a 3-year study (May 2003–Apr 2006) of mortality of northern Yellowstone elk (Cervus elaphus) calves to determine the cause for the recruitment decline (i.e., 33 calves to 13 calves/100 adult F) following the restoration of wolves (Canis lupus). We captured, fit with radiotransmitters, and evaluated blood characteristics and disease antibody seroprevalence in 151 calves ≤6 days old (68M:83F). Concentrations (x̄, SE) of potential condition indicators were as follows: thyroxine (T4; 13.8 μg/dL, 0.43), serum urea nitrogen (SUN; 17.4 mg/dL, 0.57), γ-glutamyltransferase (GGT; 66.4 IU/L, 4.36), gamma globulins (GG; 1.5 g/dL, 0.07), and insulin-like growth factor-1 (IGF-1; 253.6 ng/mL, 9.59). Seroprevalences were as follows: brucellosis (Brucella abortus; 3%), bovine-respiratory syncytial virus (3%), bovine-viral-diarrhea virus type 1 (25%), infectious-bovine rhinotracheitis (58%), and bovine parainfluenza-3 (32%). Serum urea nitrogen, GGT, GG, and IGF-1 varied with year; T4, SUN, and GG varied with age (P ≤ 0.01); and SUN varied by capture area (P = 0.02). Annual survival was 0.22 (SE = 0.035, n = 149) and varied by calving area but not year. Neonates captured in the Stephens Creek/Mammoth area of Yellowstone National Park, USA, had annual survival rates >3× higher (0.54) than those captured in the Lamar Valley area (0.17), likely due to the higher predator density in Lamar Valley. Summer survival (20 weeks after radiotagging) was 0.29 (SE = 0.05, n = 116), and calving area, absolute deviation from median birth date, and GG were important predictors of summer survival. Survival during winter (Nov-Apr) was 0.90 (SE= 0.05, n = 42), and it did not vary by calving area or year. Sixty-nine percent (n = 104) of calves died within the first year of life, 24% (n = 36) survived their first year, and 7% (n = 11) had unknown fates. Grizzly bears (Ursus arctos) and black bears (Ursus americanus) accounted for 58–60% (n = 60–62) of deaths, and wolves accounted for 14–17% (n = 15–18). Summer predation (95% of summer deaths) increased, and winter malnutrition (0% of winter deaths) decreased, compared with a similar study during 1987–1990 (72% and 58%, respectively). Physiological factors (e.g., low levels of GG) may predispose calves to predation. Also, the increase in bear numbers since wolf restoration and spatial components finer than the northern range should be considered when trying to determine the causes of the northern Yellowstone elk decline. This is the first study to document the predation impacts from reintroduced wolves on elk calf mortality in an ecosystem already containing established populations of 4 other major predators (i.e., grizzly and black bears, cougars [Puma concolor], and coyotes [Canis latrans]). The results are relevant to resource managers of the Yellowstone ecosystem in understanding the dynamics of the elk population, in providing harvest quota recommendations for local elk hunts to the Montana Department of Fish, Wildlife and Parks, the United States Fish and Wildlife Service regarding wolf and grizzly bear recovery, and to all areas worldwide where predators are increasing, by providing managers with information about potential carnivore impacts on elk populations.RESEMEN  Hemos realizado un estudio de 3 años (may 2003–abr 2006) sobre la mortalidad de las crías de wapiti (Cervus elaphus) en el norte de Yellowstone para determinar las causas del descenso del reclutamiento (de 33 a 13 crías /100 hembras adultas) tras la restauración del lobo (Canis lupus). Hemos capturado, marcado con radiotransmisores y evaluado las características de la sangre y la seroprevalencia de los anticuerpos a enfermedades de 151 crías ≤6 días (68M:83H). Las concentraciones (x̄, SE) de los indicadores del estado potencial de salud fueron: tiroxina (T4; 13.8 μg/dL, 0.43), nitrógeno de urea en suero (SUN; 17.4 mg/dL, 0.57), γ-glutamiltransferasa (GGT; 66.4 IU/L, 4.36), gamma globulinas (GG; 1.5 g/dL, 0.07) y factor de crecimiento insulinoide tipo 1 (IGF-1; 253.6 ng/mL, 9.59). Las seroprevalencias fueron: brucelosis (Brucella abortus; 3%), virus respiratorio sincitial bovino (3%), virus de la diarrea viral bovina tipo 1 (25%), rinotraqueítis infecciosa bovina (58%) y parainfluenza bovina tipo 3 (32%). El SUN, la GGT, las GG y el IGF-1 variaron con el año; la T4, el SUN y las GG variaron con la edad (P ≤ 0.01); y el SUN varió con el area decaptura (P = 0.02). La supervivencia anual fue del 0.22 (SE=0.035, n = 149) y varió con la zona de reproducción pero no con el año. Los neonatos capturados en la zona de Stephens Creek/Mammoth del Parque Nacional de Yellowstone, EE.UU., tuvieron tasas de supervivencia anual más de 3 veces superiores (0.54) a las de los capturados en la zona del valle de Lamar (0.17), presumiblemente por la mayor densidad de predadores en el valle de Lamar. La supervivencia estival (20 semanas después del radiomarcaje) fue 0.29 (SE = 0.05, n = 116); la zona de partos, la desviación absoluta de la mediana de la fecha de nacimiento y las GG fueron predictores importantes de la supervivencia estival. La supervivencia durante el invierno (nov-abr) fue 0.90 (SE= 0.05, n = 42) y no varió con la zona de partos o con el año. El 69% (n = 104) de las crías murieron antes de cumplir un año, el 24% (n = 36) sobrevivieron más de un año y se desconoce el destino del 7% (n = 11). Los osos grizzly (Ursus arctos) y los osos negros (Ursus americanus) fueron responsables del 58–60% (n = 60–62) de las muertes, y los lobos, del 14–17% (n = 15–18). La predación estival (95% de las muertes en verano) aumentó, y la malnutrición en invierno (0% de las muertes en invierno) disminuyó en comparación con un estudio similar realizado durante 1987–1990 (72% y 58%, respectivamente). Los factores fisiológicos (bajos niveles de GG) quizá predisponen a las crías a ser predadas. Además, el aumento de la población de osos desde la restauración del lobo y algunos componentes espaciales más sutiles en las montañas septentrionales deberían ser considerados al tratar de determinar las causas del declive del wapiti en el norte de Yellowstone. Este es el primer estudio que describe el impacto que la predación de lobos reintroducidos tiene sobre la mortalidad de las crías de wapiti en un ecosistema donde ya existen poblaciones establecidas de otros 4 grandes predadores (osos grizzly y negro, pumas [Puma concolor] y coyotes [Canis latrans]). Los resultados son relevantes para los gestores de recursos del ecosistema de Yellowstone porque ayudan a comprender la dinámica de las poblaciones de wapiti; aportan recomendaciones al Departamento de Pesca, Vida Silvestre y Parques de Montana para decidir cuotas de extracción de wapiti en las cacerías locales, al Servicio de Pesca y Vida Silvestre de los Estados Unidos en relación a la recuperacion del lobo y el oso grizzly; y ofrecen a los gestores información acerca de los impactos potenciales de los carnívoros sobre las poblaciones de wapiti en todas las zonas del mundo donde los predadores están aumentando.RÉSUMÉ  Nous avons realise une etude de 3 ans (mai 2003–avr 2006) portant sur les faons des wapitis du nord de Yellowstone afin de déterminer les causes du déclin de recrutement (c.-à-d. de 33 à 13 faons/100 femelles adultes) qui a suivi la réintroduction du loup (Canis lupus). Nous avons capturé, prélevé un échantillon sanguin et muni d'un radioémetteur 151 faons de ≤6 jours (68M:83F). Les concentrations (x̄, ET) d'indicateurs potentiels de condition physique étaient: thyroxine (T4; 13.8 μg/dL, 0.43), azote uréique sérique (AUS; 17.4 mg/dL, 0.57), γ-glutamyltransférase (GGT; 66.4 IU/L, 4.36), gamma globulines (GG; 1.5 g/dL, 0.07) et facteur de croissance insulinomimétique de type 1 (FCI-1; 253.6 ng/mL, 9.59). La prévalence sérique d'anticorps était: brucellose (Brucella abortus; 3%), virus syncitial respiratoire bovin (3%), virus diarrhéique bovin de type 1 (25%), rhinotrachéite infectieuse bovine (58%) et parainfluenza-3 bovin (32%). L'azote uréique sérique, la GGT, les GG et le FCI-1 ont varié entre les années; la T4, l'AUS et les GG varièrent en fonction de l'ǎge (P < 0.01) et l'AUS en fonction du lieu de capture (P = 0.02). Le taux annuel de survie atteignit 0.22 (ET = 0.035, n = 149) et varia en fonction de l'aire de mise bas mais non de l'année. Les faons nés dans l'aire de Stephens Creek/Mammoth du parc national de Yellowstone, États-Unis, possédaient des taux annuels de survie plus de 3 fois supérieurs (0.54) à ceux capturés dans l'aire de Lamar Valley (0.17), vraisemblablement à cause d'une densité de prédateurs plus élevée au second endroit. La survie estivale moyenne (20 semaines suivant le marquage) était de 0.29 (ET = 0.05, n = 116) et elle dépendait fortement du lieu de mise bas, de la déviation absolue de la date de naissance médiane et de la concentration de GG. La survie hivernale (nov-avr) atteignait 0.90 (ET= 0.05, n = 42) et ne variait ni en fonction du lieu de naissance ou de l'année. Soixante-neuf pourcent (n = 104) des faons moururent durant leur premiere année, 24% (n = 36) survécurent et le sort de 7% (n = 11) demeura inconnu. Les ours grizzlys (Ursus arctos) etles ours noirs (Ursus americanus) furent responsables de 58–60% des mortalités (n = 60–62), contre 14–17% pour les loups (n = 15–18). La prédation estivale (95% des mortalités) augmenta et la malnutrition hivernale (0% des mortalités) diminua en comparaison avec une etude similaire réalisée de 1987 à 1990 (72% et 58%, respectivement). Des facteurs physiologiques (c.-à-d. des bas niveaux de GG) pourraient prédisposer les faons à la prédation. Par ailleurs, l'accroissement du nombre d'ours depuis la réintroduction du loup et des composantes spatiales plus fines que celles de notre etude devraient ětre pris en compte en tentant de determiner les causes du déclin du nombre de wapitis du nord de Yellowstone. Notre etude s'avère la première à documenter les impacts de la prédation de loups réintroduits dans un écosystème contenant des populations établies de 4 prédateurs majeurs (c.-à-d., les ours grizzlys et noirs, les cougars [Puma concolor], les coyotes [Canis latrans]). Nos résultats concernent les gestionnaires de l'écosystème de Yellowstone puisqu'ils permettent de comprendre la dynamique de la population de wapitis, qu'ils fournissent des recommandations pour les chasses locales au Montana Department of Fish, Wildlife and Parks et d'autres, pour la gestion du loup et de l'ours grizzly, au U.S. Fish and Wildlife Service. Nos résultats concernent également toutes les regions du monde où les prédateurs s'accroissent puisqu'ils fournissent aux gestionnaires des informations concernant l'impact potentiel des carnivores sur les populations de grands herbivores.
The Eastern Prairie Population (EPP) of Canada geese (Branta canadensis interior) nests in the Hudson Bay lowlands of Manitoba and migrates through south-central Manitoba, western Minnesota, and Iowa, with a wintering terminus primarily in Missouri, Arkansas, and southern Illinois. The southern range of the EPP historically extended through Arkansas and along coastal southwestern Louisiana and Texas. However, during the 1950s and 1960s a progressive northern shift in wintering distribution occurred as numbers of geese wintering in Louisiana and Arkansas declined while numbers wintering in Missouri increased. Continued temporal and geographic shifts in fall and winter distributions were suspected during the 1980s when numbers of wintering Canada geese increased in Minnesota and declined in Missouri. However, concurrent increases in numbers of Mississippi Valley Population (MVP; B. c. interior) and Mississippi Flyway Giant Population (MFGP; B. c. maxima) Canada geese in portions of the winter range shared with EPP geese confounded interpretations of winter population and harvest surveys. During 1984-93, researchers conducted a cooperative banding and observation effort to improve information on survival rates, harvest rates, and winter distributions of EPP Canada geese. Consistent harvest regulations within 3-year periods during 1984-93, combined with extensive observations of marked geese, allowed for an integrative analysis of survival and movements of this population relative to changes in harvest pressure. We used observations, recaptures, and hunter recoveries of marked geese to provide information on survival, harvest, and movements of the EPP that is needed for long-term management of this population.Annual survival rates of neck-banded adult geese averaged (x ± SE) 0.707 ± 0.019 during 1984-86, 0.651 ± 0.022 during 1987-89 when harvest seasons were restricted, and 0.595 ± 0.028 during 1990-93 when harvest seasons were liberalized. Annual survival rates for neck-banded adults were lower versus leg-banded adults during 1987-89 and 1990-93 (P ≤ 0.05). Mean survival of neck-banded adults during the harvest seasons in 1987-89 was lower than the mean rate in the harvest seasons of 1984-86, primarily due to a low survival estimate in 1989. Survival averaged 0.918 ± 0.0129 during the 1987 and 1988 harvest seasons but declined to 0.665 ± 0.051 during 1989. Restrictions in harvest correlated with a decrease in direct recovery rates and an increase in survival rates of neck-banded adults during the 1987 and 1988 harvest seasons, but not in 1989. Higher recovery rates in 1989-92 suggested that increased harvest mortality contributed to lower survival of adult geese. However, mortality rates during the 1989-92 harvest seasons increased at a greater proportion than increases in direct recovery rates, suggesting that factors other than harvest could have significantly impacted fall mortality rates of adult geese.Estimated within-year probabilities of movement, along with population size estimates, suggested there was a northern shift in fall distributions of EPP Canada geese and delayed migrations during the late 1980s. Probabilities of southward movement for geese in the northern regions of the Flyway declined significantly during October and November when season lengths and quotas were reduced during 1987-89. While restrictions in harvest in 1987-89 corresponded with delays in fall movements, subsequent increases in harvest pressure in 1990-92 did not promote southward movement of geese in early fall. Geese that survived the harvest season in 1990-92 had lower rates of movement during October and early November than did geese that survived the harvest seasons in 1985-86. The gradual shift in the estimated timing of north-south movement, for birds known to have survived the harvest season, suggests mortality rates were higher for geese that moved south early in the fall in 1990-92. However, the lack of information on reporting rates and crippling loss for Canada geese prevented direct estimation of the proportion of fall mortality attributable to harvest.Our study demonstrated that a variety of factors can interact to affect the distribution of Canada geese and complicate approaches to population management. Information from marked geese is a critical tool for monitoring changes in survival and harvest rates of Canada goose populations, especially in light of recent changes in winter distributions and resultant mixing of populations. Data for EPP Canada geese indicated that neck-banded geese had lower survival and higher recovery rates than did leg-banded geese. If harvest was the major source of mortality for EPP geese, our results suggested that actual reporting rates for Canada geese were lower than rates estimated for mallards (Anas platyrhynchos). In contrast, if harvest was not the major source of mortality for geese, then managers need to consider nonharvest mortality rates when determining optimal harvest rates for sustainable populations of Canada geese. In light of recent changes in band inscriptions designed to increase reporting rates, we recommend that managers limit the use of neck bands and that monitoring programs for Canada geese be designed to minimize potential biases due to colored auxiliary markers and differential reporting rates. We also recommend that band reporting rates be evaluated for goose populations across North America. Information on temporal and spatial differences in reporting rates would improve management efforts for EPP Canada geese by allowing a better understanding of the relative impacts of harvest and nonharvest mortality rates.
Several potential proximate causes may be implicated in a recent (post-1984) decline in moose (Alces alces andersoni) numbers at their southern range periphery in northwest Minnesota, USA. These causes include deleterious effects of infectious pathogens, some of which are associated with white-tailed deer (Odocoileus virginianus), negative effects of climate change, increased food competition with deer or moose, legal or illegal hunting, and increased predation by gray wolves (Canis lupus) and black bears (Ursus americanus). Long-standing factors that may have contributed to the moose decline include those typically associated with marginal habitat such as nutritional deficiencies. We examined survival and productivity among radiocollared (n = 152) adult female and juvenile moose in northwest Minnesota during 1995–2000, and assessed cause of death and pathology through carcass necropsy of radiocollared and non-radiocollared animals.
Military lands are a valuable resource in recovery of threatened, endangered, and at-risk species worldwide and have the highest density of threatened and endangered species of all major land management agencies in the United States. Many red-cockaded woodpeckers (Picoides borealis) that reside on federal lands occur on 15 military installations in the southeastern United States. This close association has increased concern over potential conflicts between conservation requirements of endangered species and the military's mission of combat readiness. Our objectives were to 1) determine if military training operations affect behavior, reproductive success, and productivity of red-cockaded woodpeckers; 2) develop a frequency-weighting function to assess woodpecker hearing sensitivity; 3) identify factors that affect woodpecker responses to military training operations; 4) develop distance and dose-response thresholds for quantifying woodpecker responses to noise levels and stimulus distances; 5) characterize military training operations through quantification of sound levels, source identification, distance from active woodpecker nests, frequency spectra, duration, and frequency of occurrence; and 6) document baseline woodpecker nesting behavior. We conducted our study on the Fort Stewart Military Installation located in southeast Georgia, USA.
The Mid-continent Population (MCP) of sandhill cranes (Grus canadensis) is widely hunted in North America and is separated into the Gulf Coast Subpopulation and Western Subpopulation for management purposes. Effective harvest management of the MCP requires detailed knowledge of breeding distribution of subspecies and subpopulations, chronology of their use of fall staging areas and wintering grounds, and exposure to and harvest from hunting. To address these information needs, we tagged 153 sandhill cranes with Platform Transmitting Terminals (PTTs) during 22 February-12 April 1998-2003 in the Central and North Platte River valleys of south-central Nebraska. We monitored PTT-tagged sandhill cranes, hereafter tagged cranes, from their arrival to departure from breeding grounds, during their fall migration, and throughout winter using the Argos satellite tracking system. The tracking effort yielded 74,041 useable locations over 49,350 tag days; median duration of tracking of individual cranes was 352 days and 73 cranes were tracked > 12 months. Genetic sequencing of mitochondrial DNA (mtDNA) from blood samples taken from each of our random sample of tagged cranes indicated 64% were G. c. canadensis and 34% were Grus canadensis tabida. Tagged cranes during the breeding season settled in northern temperate, subarctic, and arctic North America (U. S. [23%, n = 35], Canada [57%, n = 87]) and arctic regions of northeast Asia (Russia [20%, n = 31]). Distribution of tagged cranes by breeding affiliation was as follows: Western Alaska-Siberia (WA-S, 42 +/- 4% [SE]), northern Canada-Nunavut (NC-N, 21 +/- 4%), West-central Canada-Alaska (WC-A, 23 +/- 4%) and East-central Canada-Minnesota (EC-M, 14 +/- 3%). All tagged cranes returned to the same breeding affiliation used during the previous year with a median distance of 1.60 km (range: 0.08-7.7 km, n - 53) separating sites used in year 1 and year 2. Fall staging occurred primarily in central and western Saskatchewan (69%), North Dakota (16%), southwestern Manitoba (10%), and northwestern Minnesota (3%). Space-use sharing indices showed that except for NC-N and WC-A birds, probability of finding a crane from one breeding affiliation within the home range of another breeding affiliation was low during fall staging. Tagged cranes from WC-A and EC-M breeding affiliations, on average, spent 25 and 20 days, respectively, longer on fall staging areas in the northern plains than did WA-S and NC-N birds. Cranes in the NC-N, WA-S, and WC-A affiliations spent 99%, 74%, and 64%, respectively, of winter in western Texas in Hunting Zone A; EC-M cranes spent 83% of winter along the Texas Gulf Coast in Hunting Zone C. Tagged cranes that settled within the breeding range of the Gulf Coast Subpopulation spent 28% and 42% of fall staging and winter within the range of the Western Subpopulation, indicating sufficient exchange of birds to potentially limit effectiveness of MCP harvest management. Harvests of EC-M and WC-A cranes during 1998-2003 were disproportionately high to their estimated numbers in the MCP, suggesting more conservative harvest strategies may be required for these subpopulations in the future, and for sandhill cranes to occupy major parts of their historical breeding range in the Prairie Pothole Region. Exceptionally high philopatry of MCP cranes of all 4 subpopulations to breeding sites coupled with strong linkages between crane breeding distribution, and fall staging areas and wintering grounds, provide managers guidance for targeting MCP crane harvest to meet management goas. Sufficient temporal or spatial separation exists among the 4 subpopulations on fall staging areas and wintering grounds to allow harvest to be targeted at the subpopulation level in all states and provinces (and most hunting zones within states and provinces) when conditions warrant. Knowledge gained from our study provides decision-makers in the United States, Canada, Mexico, and Russia with improved guidance for developing sound harvest regulations, focusing conservation efforts, and generating collaborative efforts among these nations on sandhill crane research and management to meet mutually important goals. (c) 2011 The Wildlife Society.
Manipulating predator populations is often posed as a solution to depressed ungulate populations. However, predator–prey dynamics are complex and the effect on prey populations is often an interaction of predator life history, climate, prey density, and habitat quality. The effect of predator removal on ungulate and, more specifically, mule deer (Odocoileus hemionus) populations has not been adequately investigated at a management scale. We tested the efficacy of removing coyotes (Canis latrans) and mountain lions (Puma concolor) for increasing survival and population growth rate of mule deer in southeastern Idaho, USA, during 1997–2003. We assigned 8 game management units (GMUs) to treatments under a 2 × 2 factorial design (treatments of coyote removal and lion removal) with 2 replicates of each treatment or reference area combination. We used methods typically available to wildlife managers to achieve predator removals and a combination of extensive and intensive monitoring in these 8 GMUs to test the hypothesis that predator removal increased vital rates and population growth rate of mule deer. We determined effects of predator removal on survival and causes of mortality in 2 intensive study sites, one with coyote and mountain lion removal and one without. We also considered the effects of other variables on survival including lagomorph abundance and climatic conditions. In these 2 intensive study areas, we monitored with radiotelemetry 250 neonates, 284 6-month-old fawns, and 521 adult females. At the extensive scale, we monitored mule deer population trend and December fawn ratios with helicopter surveys. Coyote removal decreased neonate mortality only when deer were apparently needed as alternate prey, thus removal was more effective when lagomorph populations were reduced. The best mortality model of mule deer captured at 6 months of age included summer precipitation, winter precipitation, fawn mass, and mountain lion removal. Over-winter mortality of adult female mule deer decreased with removal of mountain lions. Precipitation variables were included in most competing mortality models for all age classes of mule deer. Mountain lion removal increased fawn ratios and our models predicted fawn ratios would increase 6% at average removal rates (3.53/1,000 km2) and 27% at maximum removal rates (14.18/1,000 km2). Across our extensive set of 8 GMUs, coyote removal had no effect on December fawn ratios. We also detected no strong effect of coyote or mountain lion removal alone on mule deer population trend; the best population-growth-rate model included previous year's mountain lion removal and winter severity, yet explained only 27% of the variance in population growth rate. Winter severity in the current and previous winter was the most important influence on mule deer population growth. The lack of response in fawn ratio or mule deer abundance to coyote reduction at this extensive (landscape) scale suggests that decreased neonate mortality due to coyote removal is partially compensatory. Annual removal of coyotes was not an effective method to increase mule deer populations in Idaho because coyote removal increased radiocollared neonate fawn survival only under particular combinations of prey densities and weather conditions, and the increase did not result in population growth. Coyote-removal programs targeted in areas where mortality of mule deer fawns is known to be additive and coyote-removal conditions are successful may influence mule deer population vital rates but likely will not change direction of population trend. Although mountain lion removal increased mule-deer survival and fawn ratios, we were unable to demonstrate significant changes in population trend with mountain lion removal. In conclusion, benefits of predator removal appear to be marginal and short term in southeastern Idaho and likely will not appreciably change long-term dynamics of mule deer populations in the intermountain west. © 2011 The Wildlife Society.La manipulación de las poblaciones de depredadores se plantea a menudo como una solución para reducir las poblaciones de ungulados. Sin embargo, las dinámicas depredador-presa son complejas y el efecto sobre las poblaciones de presas es a menudo una interacción entre depredador, historia de vida, clima, densidad de presas y calidad del hábitat. El efecto de la eliminación de depredadores en ungulados y, más concretamente, en la población de ciervo mula (Odocoileus hemionus) no ha sido adecuadamente investigado con una perspectiva de gestión. Pusimos a prueba la eficacia de la eliminación de coyotes (Canis latrans) y pumas (Puma concolor) para aumentar la supervivencia y la tasa de crecimiento de la población de venados en el sureste de Idaho, USA, durante el periodo 1997–2003. Se asignaron ocho unidades de gestión de la caza (GMU) a los tratamientos bajo un diseño factorial 2 × 2 (tratamientos de eliminación de coyote y eliminación de pumas) con dos repeticiones de cada tratamiento o combinación de zona de referencia. Se utilizaron métodos comunmente disponibles a los gestores de la fauna silvestre para el traslado de depredadores y una combinación de vigilancia extensiva e intensiva en estas 8 GMU para probar la hipótesis de que la eliminación de depredadores aumenta las tasas vitales y la tasa de crecimiento de la población del ciervo mula. Se determinaron los efectos de la eliminación de depredadores en la supervivencia y las causas de mortalidad en los dos sitios de estudio intensivo, uno con la eliminación de ambos, pumas y coyotes y el otro sin dicha eliminación. También se consideraron los efectos de otras variables en la supervivencia, como la abundancia de lagomorfos y las condiciones climáticas. En estas dos áreas de estudio intensivo, monitorizamos con radiotelemetría 250 recién nacidos, 284 cervatillos de 6 meses de edad, y 521 hembras adultas. En una escala espacial mas amplia, monitorizamos la tendencia de la población de ciervo mula y la tasa de supervivencia de cervatillos en el mes de Diciembre con censos realizados desde un helicóptero. La eliminación de coyotes reducio la mortalidad neonatal sólo cuando los ciervos se necesitaban como presa alternativa, por lo que la eliminación fue más eficaz cuando las poblaciones de lagomorfos se redujeron. El mejor modelo de mortalidad de venados capturados a los 6 meses de edad fué el que incluía precipitación de verano, precipitacion de invierno, masa cervatillo, y eliminación del león de montaña. Durante el invierno la mortalidad de venados hembra adultas disminuyó con la eliminación de pumas. Las variables relativas a precipitación se incluyeron en la mayoría de los modelos de mortalidad para todas las clases de edad de ciervo mula. La eliminación de pumas aumento la tasa de cervatillos y los modelos predijeron el 6% de incremento en la tasa de cervatillo para una tasa de extracción media (3,53/1.000 km2) y 27% para una tasa de extracción máxima (14,18/1.000 km2). La eliminación de coyotes no tuvo ningún efecto sobre los coeficientes de cervatillo de diciembre en ninguno de los 8 GMU. Tampoco se detectó ningún efecto de la eliminación de coyotes o pumas en la tendencia numerica de la población de ciervos mula, el modelo con la tasa de crecimiento más alta era el que incluyó los pumas eliminados el año anterior y la gravedad del invierno, sin embargo, sólo explicó el 27% de la varianza en la tasa de crecimiento de la población. La severidad del invierno en el año actual y anterior fue la influencia más importante en el crecimiento de población de ciervos mula. La falta de respuesta en la tasa de abundancia de cervatillo o de venados a la reducción de coyote en esta extensa escala sugiere que la disminución de la mortalidad neonatal debida a la eliminación de coyote es parcialmente compensatoria. La extracción anual de coyotes no era un método eficaz para aumentar las poblaciones de ciervo mula en Idaho porque la eliminación de coyote aumento la supervivencia de cervatillos con radiocollares sólo bajo determinadas combinaciones de densidades de presas y condiciones meteorológicas, y el aumento no se tradujo en un crecimiento de la población. Los programas específicos de eliminación de coyotes en las áreas donde se sabe que la mortalidad de ciervo mula es aditiva y en las que las condiciones de extracción de los coyotes tienen éxito, pueden influir en las tasas vital de población de ciervo mula, pero probablemente no van a cambiar la tendencia numerica de la población. Aunque la reducion de pumas aumentó la sobrevivencia de ciervos mula y la tasa de cervatillos, no hemos podido demostrar cambios significativos en la tendencia de la población con la eliminación de pumas. En conclusión, los beneficios de la eliminación de depredadores parecen ser marginal y a corto plazo en el sureste de Idaho, y no van a cambiar sensiblemente la dinámica a largo plazo de las poblaciones de ciervo mula en el oeste montañoso de los Etados Unidos. © The Wildlife Society, 2011.La manipulation des populations de prédateurs est souvent proposée comme une solution pour réduire les populations d'ongulés. Cependant, les dynamiques prédateur-proie sont complexes et l'effet sur les populations de proies est souvent une interaction entre le cycle de vie du prédateur, le climat, la densité des proies et la qualité de l'habitat. L'effet de la suppression du prédateur sur les populations d'ongulés et, plus spécifiquement, de cerf mulet (Odocoileus hemionus) n'a jamais été étudié de façon satisfaisante pour un objectif de gestion. Nous avons testé l'efficacité de la suppression des coyotes (Canis latrans) et des pumas (Puma concolor) sur l'augmentation de la survie et du taux de croissance de la population de cerf mulet dans le sud-est de l'Idaho, États-Unis, de 1997 à 2003. 8 unités de jeu de gestion (GMUs) ont été soumises aux traitements selon un plan factoriel 2 × 2 (traitements de suppression du coyote et de suppression du puma) avec 2 répétitions de chaque combinaison de traitement ou de zone de référence. Nous avons utilisé des méthodes que les gestionnaires de la faune ont généralement à disposition pour effectuer les retraits de prédateurs et la combinaison de surveillances extensive et intensive dans ces 8 GMUs afin de tester l'hypothèse selon laquelle le retrait des prédateurs augmente le taux vital et le taux de croissance de la population de cerf mulet. Les effets de la suppression des prédateurs sur la survie et les causes de mortalité ont été déterminés dans les deux sites d'étude intensive, l'un avec le retrait des pumas et des coyotes et l'autre sans. Les effets sur la survie d'autres variables, incluant l'abondance des lagomorphes et les conditions climatiques, ont été examinés. Dans ces deux zones d'étude intensive, nous avons suivi par radio-télémétrie 250 nouveau-nés, 284 faons de 6 mois, et 521 femelles adultes. À plus grande échelle, la tendance démographique de cerf mulet et le ratio de faons en Décembre ont été suivis par hélicoptère. L'élimination des coyotes diminue la mortalité néonatale seulement lorsque les cerfs semblent nécessaires comme proies alternatives, ainsi le retrait des coyotes est plus efficace lorsque les populations de lagomorphes sont réduites. Le meilleur modèle de mortalité des cerfs mulet à 6 mois d'âge obtenu inclue les précipitations estivales et hivernales, la masse des faons, et le retrait du puma. La mortalité hivernale des biches adultes diminue avec la suppression des pumas. Les variables liées aux précipitations sont incluses dans la plus part des modèles de mortalité pour toutes les classes d'âge de cerf mulet. La suppression des pumas augmente le ratio de faons et nos modèles prédisent une augmentation de 6% du ratio de faons pour des taux de retrait moyens (3,53/1,000 km2) et de 27% pour des taux de retrait maximum (14,18/1,000 km2). La suppression du coyote n'a eu aucun effet sur les ratios de faons de Décembre pour les 8 GMUs extensives. Aucun effet important du retrait du coyote ou du puma seul sur la tendance démographique des cerfs mulet n'a été détecté; le meilleur modèle de taux de croissance de la population inclut le retrait des pumas l'année précédente et la sévérité de l'hiver, qui cependant n'explique que 27% de la variance du taux de croissance de la population. La sévérité de l'hiver de l'année en cours et de la précédente est la variable la plus influente sur la croissance de la population de cerfs mulets. L'absence de réponse du ratio de faons et de l'abondance du cerf mulet à la réduction des coyotes pour une large échelle (paysage) suggère que le déclin de la mortalité néonatale du à la suppression du coyote est partiellement compensé. Le retrait annuel des coyotes n'est pas une méthode efficace pour accroître les populations de cerfs mulets dans l'Idaho car la suppression du coyote a augmenté la survie des faons suivis pas radio-télémétrie seulement sous certaines combinaisons de densité des proies et de conditions météorologiques, et l'augmentation ne se traduit pas par une croissance démographique. Les programmes de retrait du coyote ciblant les zones où la mortalité des faons est connue pour être additive et où les conditions permettent un retrait du coyote avec succès, peuvent influencer les taux vitaux de la population de cerfs mulet, mais ne changera probablement pas le sens de la tendance démographique. Bien que le retrait des pumas augmente la survie des cerfs mulet et le ratio de faons, nous n'avons pas pu démontrer de changement significatif dans les tendances démographiques après élimination des pumas. En conclusion, les avantages de la suppression des prédateurs semblent être marginaux et à court terme dans le sud-est de l'Idaho et ne modifieront pas sensiblement les dynamiques à long terme des populations de cerf mulet dans l'ouest montagneux des Etats-Unis.
The threatened population of Atlantic Coast piping plovers (Charadrius melodus) has increased under intensive management of predation and disturbance. However, the relative importance of habitat quality, nest predation, and chick predation in population dynamics and reproductive success of this species are poorly understood. We examined effects of breeding-habitat alterations, predation, and breeding phenology on population size, habitat use, and reproductive output of piping plovers from 1993 to 2004. We studied piping plovers at a newly colonized site (West Hampton Dunes [WHD]) on a New York, USA, barrier island, and an adjacent reference site (REF) with a long-standing population. We monitored population size and reproductive success; determined chick habitat use and behavior; and monitored changes in habitat availability, prey abundance, and predator presence. Resource agencies managed predation by mammal trapping and by fencing nests with predator exclosures in some years. Following storm- and human-related increases in nesting and foraging habitat, the population at WHD grew from 5 pairs in 1993 to 39 pairs in 2000. The WHD population then declined to 18 pairs by 2004 concurrent with habitat losses to human development. In contrast, the population size at REF was not correlated with nesting habitat area. Population growth rate decreased with density at WHD but not at REF, which was likely close to equilibrium when the study began. Neither reproductive output nor any of its components were correlated with population density, and reproductive output was correlated between the sites despite their different population trajectories, suggesting that the population was primarily regulated by adult survival, emigration, or immigration. The latter 2 factors should be especially sensitive to local habitat quality, and the main differences between our sites was that bayside intertidal flats were available adjacent to nesting habitat at WHD but not at REF, and that a village construction project took place at WHD. Clutch size and renest rate decreased over the breeding season. Predator exclosures improved nest daily survival, and mammal trapping improved chick daily survival. Chick foraging rate was highest in bayside intertidal flats and in ocean- and bayside fresh wrack. Chicks used the bay side more than expected from percentage habitat area, and survived better on the bay side before village construction and the initiation of predator trapping, but not after. At both sites, number of chicks fledged per pair was lowest for pairs that nested late and lost a nest late in the season and increased with the annual number of cats (Felis catus) and foxes (Vulpes vulpes) trapped. Restoring nesting habitat adjacent to bayside intertidal flats may increase the carrying capacity (nesting pairs) at piping plover breeding sites. However, without predation management, restored sites may not contribute many recruits to the regional population.RESUMENLas poblaciones amenazadas de frailecillo silbadór (Charadrius melodus) de la Costa Atlántico se han incrementado bajo un manejo intensivo de las perturbaciones y la depredación. Sin embargo, hay poco entendimiento acerca de la importancia relativa de la calidad del hábitat, la depredación en nidos y la depredación en polluelos sobre la dinámica poblacional y el éxito reproductivo de esta especie. Examinamos los efectos de las alteraciones del hábitat de reproducción, la depredación y la fenología reproductiva sobre el tamaño de población de frailecillos silbadóres, además del uso de hábitat y el rendimiento reproductivo, durante 1993 a 2004. Estudiamos frailecillos silbadóres en un sitio recientemente colonizado (West Hampton Dunes, WHD) en una isla-barrera en Nueva York, así como en un sitio de referencia adyacente (REF) con una población persistente. Monitoreamos el tamaño de población y el éxito reproductivo, determinamos el uso de hábitat por los polluelos y su comportamiento, y monitoreamos los cambios en la disponibilidad de hábitat, la abundancia de presas y la presencia de depredadores. Las instituciones de recursos manejaron la depredación mediante la captura de mamíferos, y la protección de nidos con cercas para excluir a los depredadores durante algunos años. La población de frailecillos de WHD se incrementó de 5 parejas en 1993 a 39 parejas en 2000 enseguida de las tormentas y el incremento del hábitat de forrajeo y anidación relacionado con el hombre. La población declinó a 18 parejas hacia el 2004, simultáneamente con la perdida de hábitat causada por asentamientos humanos. En cambio, el tamaño de la población de referencia REF no se correlacionó con el área del hábitat de anidación. La tasa de crecimiento poblacional disminuyó con la densidad en WHD pero no en REF, la cual probablemente estaba cercana al equilibrio al comienzo del estudio. Ni el resultado reproductivo ni sus componentes se correlacionaron con la densidad poblacional, sin embargo, el resultado reproductivo se correlacionó entre los sitios a pesar de sus diferentes trayectorias poblacionales, sugiriendo que las poblaciones se regularon primordialmente por la supervivencia de los adultos, la emigración y/o la inmigración. Estos dos últimos factores serían especialmente sensitivos a la calidad local del hábitat. Las principales diferencias entre nuestros sitios fueron la disponibilidad de terrenos mesolitorales planos adyacentes al hábitat de anidación en WHD pero no en REF, y la construcción de un asentamiento humano en WHD. El tamaño de nidada y la tasa de reanidación disminuyeron durante la temporada reproductiva. Las cercas anti-depredadores mejoraron la supervivencia diaria de los nidos, y la captura de mamíferos mejoró la supervivencia diaria de los polluelos. La tasa de forrajeo de los polluelos fue mayor en las bahías mesolitorales planas y en las áreas oceánicas y ensenadas con macroalgas frescas. Los polluelos usaron las bahías más de lo esperado respecto al porcentaje de hábitat, y su supervivencia fue superior en las bahías antes de la construcción del asentamiento y al inicio de la captura de mamíferos, pero no después. En ambos sitios, el número de volantones por pareja fue mas bajo en aquellas parejas que anidaron tardíamente y perdieron una nidada al final de la estación, y aumentó con el número anual de gatos y zorros atrapados. La restauración del hábitat de anidación adyacente a las bahías mesolitorales planas puede incrementar la capacidad de carga (parejas anidando) en los sitios de reproducción de frailecillos silbadóres. Sin embargo, sin un manejo de control de depredadores, los sitios restaurados podrían no contribuir con reclutamientos considerables a la población local.RÉSUMÉLa population menacée du Pluvier siffleur de la cǒte Atlantique (Charadrius melodus) a augmenté grǎce au contrǒle intensif de la prédation et des perturbations. Cependant, l'importance relative de la qualité de l'habitat, de la prédation des nids, et de la prédation des oisillons dans la dynamique de la population et dans le succès de reproduction de cette espèce sont mal compris. Nous avons examiné l'impact de l'altération des habitats de reproduction, de la prédation, et de la phénologie de la nidification sur la taille de la population, l'usage de l'habitat, et le succès de reproduction du Pluvier siffleur entre 1993 et 2004. Nous avons étudié le Pluvier siffleur à un site nouvellement colonisé (West Hampton Dunes, WHD) sur une ǐle-barrière au New York, et à un site de référence avoisinant (REF) dont la population était établie depuis longtemps. Nous avons effectué le suivi des populations et le succès de reproduction; déterminé le comportement et l'utilisation de l'habitat des oisillons; et relevé les changements dans la disponibilité de l'habitat, l'abondance des proies, et la présence des prédateurs. Les agences de ressource ont géré la prédation en piégeant les mammifères et en utilisant des exclos sur les nids dans certaines années. Suivant l'amelioration des habitats de nidification et d'alimentation causée par des tempětes et des facteurs anthropiques, la population de WHD a augmenté de 5 couples en 1993 à 39 couples en 2000. La population de WHD a ensuite diminué jusqu'à 18 couples en 2004 suite à la perte d'habitat causé par le développement cǒtier. Par contre, la taille de la population à REF n'était pas corrélée avec la superficie de l'habitat de nidification. Le taux de croissance de la population a diminué avec la densité à WHD mais pas à REF, où la population était proche de l'équilibre quand l'é tude a commencé. Ni le succès de reproduction ni aucune de ses composantes n'a été corrélé avec la densité de la population, et le succès de reproduction a été corrélé entre les sites malgré leur différentes trajectoires de population, suggérant que la population était principalement régulée par la survie des adultes, l'émigration et/ou l'immigration. Les derniers deux facteurs devraient ětre spécialement sensible à la qualité de l'habitat local, et les principales différences entre nos sites étaient que les estrans du littoral de la baie étaient disponibles contigu à l'habitat de nidification à WHD mais pas à REF, et qu'un projet de construction d'un village a eu lieu à WHD. La taille de la ponte et le taux de renidification a diminué durant la saison de reproduction. Les exclos ont améliore la survie quotidienne des nids, et le piégeage des mammifères a améliore la survie quotidienne des oisillons. Le taux d'alimentation des oisillons était plus élevé dans les estrans du littoral du cǒté de la baie et dans la zone de varech fraǐche à l'océan et au cǒté de la baie. Les oisillons ont utilisé le cǒté de la baie plus que prévu du % de la superficie de l'habitat, et ont mieux survécu du cǒté de la baie avant la construction du village et l'initiation du piégeage des prédateurs, mais pas par après. Aux deux sites, le nombre d'oisillons survivant à l'envol par couple était plus bas pour les couples qui ont niché tard et qui ont perdu leur nid tard dans la saison, et a augmenté avec le nombre de chats et de renards piégés par année. La restauration des habitats de nidification contigu aux estrans du littoral du cǒté de la baie pourrait augmenter la capacité de support (couples nicheurs) aux sites de reproduction du Pluvier siffleur. Par contre, sans la gestion de la prédation, les sites restaurés ne contribueront probablement pas beaucoup de recrues à la population régionale.
Concerns over declining mule deer (Odocoileus hemionus) populations during the 1990s prompted research efforts to identify and understand key limiting factors of deer. Similar to past deer declines, a top priority of state wildlife agencies was to evaluate the relative importance of habitat and predation. We therefore evaluated the effect of enhanced nutrition of deer during winter and spring on fecundity and survival rates using a life table response experiment involving free-ranging mule deer on the Uncompahgre Plateau in southwest Colorado, USA. The treatment represented an instantaneous increase in nutritional carrying capacity of a pinyon (Pinus edulis)—Utah juniper (Juniperus osteosperma) winter range and was intended to simulate optimum habitat quality. Prior studies on the Uncompahgre Plateau indicated predation and disease were the most common proximate causes of deer mortality. By manipulating nutrition and leaving natural predation unaltered, we determined whether habitat quality was ultimately a critical factor limiting the deer population. We measured annual survival and fecundity of adult females and survival of fawns, then estimated population rate of change as a function of enhanced nutrition. Pregnancy and fetal rates of adult females were high and did not vary in response to treatment. Fetal and neonatal survival rates increased in response to treatment, although the treatment effect on neonatal survival was marginal. Overwinter rates of fawn survival increased for treatment deer by 0.16–0.31 depending on year and fawn sex, and none of the 95% confidence intervals associated with the effects overlapped zero. Overwinter rates of fawn survival averaged 0.905 (SE = 0.026) for treatment deer and 0.684 (SE = 0.044) for control deer. Nutritional enhancement increased survival rates of fetuses to the yearling age class by 0.14–0.20 depending on year and fawn sex; 95% confidence intervals slightly overlapped zero. When averaging estimates across sexes and years, treatment caused fetal to yearling survival to increase by 0.177 (SE = 0.082, 95% CI: 0.016–0.337). Annual survival of adult females receiving treatment (Ś = 0.879, SE = 0.021) was higher than survival of control adult females (Ś = 0.833, SE = 0.025). Our estimate of the population rate of change (λ) was 1.165 (SE = 0.036) for treatment deer and 1.033 (SE = 0.038) for control deer. Increased production and survival of young (i.e., fetal, neonatal, and overwinter fawn survival) accounted for 64% of the overall increase in λ, whereas adult female survival accounted for 36% of the increase in λ. The effect of nutrition treatment on overwinter fawn survival alone accounted for 33% of the overall increase in λ.We documented food limitation in the Uncompahgre deer population because survival of fawns and adult females increased considerably in response to enhanced nutrition. We found strong evidence that enhanced nutrition of deer reduced coyote (Canis latrans) and mountain lion (Puma concolor) predation rates of ≥6-month-old fawns and adult females. Our results demonstrate that observed coyote predation, by itself, is not useful for evaluating whether coyotes are negatively impacting a deer population. Our results also indicate that mountain lions may select for deer in poorer condition under some circumstances, suggesting that mountain lion predation may not always be an additive source of mortality. Disease mortality rates of adult females did not decline in response to enhanced nutrition. Winter-range habitat quality was a limiting factor of the Uncompahgre Plateau mule deer population. Therefore, we recommend evaluating habitat treatments for deer that are designed to set-back succession and increase productivity of late-seral pinyon-juniper habitats that presently dominate the winter range.RESUMENPreocupaciones sobre disminuciones poblacionales de venados bura (Odocoileus hemionus) durante los años noventa han incitado esfuerzos de investigación para identificar y entender los factores claves limitantes de los venados. Semejante a disminuciones pasadas de los venados, la prioridad alta de las autoridades estatales era evaluar la importancia relativa del hábitat y la depredación. Por lo tanto, evaluamos el efecto de la nutrición aumentada de venados durante invierno y primavera en las tasas de fecundidad y supervivencia utilizando un experimento de respuesta de tabla de vida involucrando venados bura silvestres de la Meseta de Uncompahgre en el sudoeste de Colorado. El tratamiento representó un aumento instantáneo en la capacidad nutricional en una área invernal dominado por piñon (Pinus edulis) y enebro de Utah (Juniperus osteosperma), y fue pretendido simular la calidad óptima del hábitat. Estudios previos en la Meseta de Uncompahgre indicaron que la depredación y la enfermedad fueron las causas más comunes de la mortalidad de venados. Determinamos si la calidad del hábitat fue últimamente un factor limitante crítico de la población de venados por manipular la nutrición y dejar la depredación como fue. Medimos fecundidad y la supervivencia anual de hembras adultas y la supervivencia de los cervatos, entonces estimado la tasa de cambio poblacional en función de nutrición aumentada. El embarazo y las tasas fetales de hembras adultas eran altos y no variaron en respuesta al tratamiento. Las tasas de supervivencia fetales y neonatales aumentaron en respuesta al tratamiento, aunque el efecto del tratamiento sobre supervivencia neonatal fuera marginal. La supervivencia de ciervos por invierno fue considerablemente más alto entre venados del tratamiento que venados de control. La supervivencia de invierno incrementó por 0.16–0.31, dependiendo del año y sexo de cervato, y ninguno de los intervalos de confianza de 95% asociado con el efecto incluyó 0. La supervivencia de cervatos por invierno promediado 0.905 (EE=0.026) para venados de tratamiento y 0.684 (EE=0.044) para venados de control. El tratamiento de nutrición aumentada incrementó la supervivencia de fetos a la edad añal por 0.14–0.20 dependiendo de año y sexo de cervato, aunque los intervalos de confianza de 95% asociado con el efecto apenas incluyó 0. Al promediar las estimaciones a través de sexos y años, el tratamiento causó supervivencia de fetos a la edad añal incrementar por 0.177 (EE = 0.082, IC 95%: 0.016, 0.337). Supervivencia de venados hembras recibiendo el tratamiento (Ś = 0.879, EE = 0.021) fue más alto que la supervivencia de venados controles (Ś = 0.833, EE = 0.025). Nuestra estimación de la tasa de cambio poblacional, λ, fue 1.165 (EE = 0.036) para venados tratados y 1.033 (EE = 0.038) para venados controles. La supervivencia por invierno de crías (i.e, supervivencia fetal-neonatal-ciervos pro invierno) explicó 64% del aumento global en λ, mientras que la supervivencia de los venados hembras adultas explicó 36% del aumento en λ. El efecto del tratamiento de nutrición en la supervivencia de ciervos por invierno solo explicó 33% del aumento global en λ.Documentamos limitación de alimento en la población de venados de la Uncompaghre porque la supervivencia de los ciervos y las venados hembras incrementó considerablemente en respuesta a la nutrición aumentada. Encontramos evidencia fuerte que nutrición aumentada de venados redujó depredación por coyotes (Canis latrans) y pumas (Puma concolor) en ciervos ≥6 meses de edad y en venados hembras. Nuestros resultados demuestran que depredación por coyotes observada, sola, no es útil para evaluar si los coyotes impactan negativamente a una población de venados. Nuestros resultados indican también que las pumas pueden seleccionar venados en peor condición bajo algunas circunstancias, sugeriendo que depredación por pumas no siempre puede ser una fuente aditiva de la mortalidad. Las tasas de mortalidad por enfermedad de venados hembras no disminuyeron en respuesta a la nutrición aumentada. Calidad del habitat en el área invernal fue un factor limitante de la población de venados bura de la Meseta Uncompahgre. Por lo tanto, recomendamos evaluar tratamientos del hábitat para venados que son diseñados para retrasar la sucesión y incrementar la productividad de los habitats del piñon-enebro en etapas avanzadas de sucesión los cuales actualmente dominan la área invernal.RÉSUMÉL'inquiétude concernant le déclin des populations de cerf mulet (Odocoileus hemionus) durant les années 1990 a orienté les efforts de recherche vers l'identification et la compréhension des facteurs limitant ces populations. Lors des précédents déclins, l'une des priorités des agences d'état en charge de la faune sauvage a porté sur l'évaluation de l'importance relative de l'habitat et de la prédation. C'est pourquoi nous avons évalué l'impact d'un complément d'alimentation en hiver et au printemps sur les taux de fécondité et de survie, grǎce à une analyse démographique impliquant des cerfs mulets en liberté sur le Plateau Uncompahgre, dans le sud-ouest du Colorado. Le complément de nutrition peut ětre considéré comme un accroissement immédiat de la capacité d'accueil de l'aire d'extension hivernale dont l'habitat est composé de pins du Colorado (Pinus edulis) et de genévriers (Juniperus osteosperma). Ce traitement visait à simuler un habitat de qualité optimale. Des études préliminaires sur le Plateau de Uncompahgre ont montré que la prédation et les maladies sont les principales causes immédiates de mortalité du cerf mulet. En manipulant la nutrition et en laissant la prédation inchangée, nous avons déterminé si la qualité de l'habitat constituait un facteur limitant la performance de la population. Nous avons mesuré la fécondité et la survie annuelle des femelles adultes et la survie des faons. Nous avons ensuite utilisé ces paramètres pour estimer le taux de croissance de la population en presence ou non de complément alimentaire. Les taux de gestation et le nombre moyen de foetus des femelles adultes étaient élevés et ne variaient pas dans la réponse au traitement. Le taux de survie foetale et néonatale a augmenté en réponse au traitement, bien que l'effet du traitement sur la survie néonatale ait été marginal. Le taux de survie hivernale des faons était nettement plus élevé pour les cerfs ayant reçu l'apport nutritionel que pour les cerfs ayant servi de témoin. La survie hivernale des faons a augmenté de 0.16–0.31, suivant l'année et le sexe du faon, et aucun des intervalles de confiance à 95% associés à l'effet n'incluait 0. La survie hivernale des faons était en moyenne 0.905 (SE = 0.026) pour les cerfs de traitement et 0.684 (SE = 0.044) pour les cerfs de contrǒle. L'amélioration nutritionnelle a augmenté le taux de survie des foetus ǎgés de 1 an de 0.14?0.20, suivant l'année et le sexe, bien que l'intervalle de confiance à 95% incluait 0. En faisant une moyenne des estimations sur les sexes et les années, le traitement d'apport nutritionel a permis une augmentation de la survie depuis le stade foetal jusqu'à deux ans de 0.177 (SE = 0.082, 95% CI: 0.016, 0.337). Le complément alimentaire a également eu un effet positif sur la survie des femelles adultes. La survie des femelles ayant reçu le traitement (Ś = 0.879, SE = 0.021) était supérieure à la survie des individus témoins (Ś = 0.833, SE = 0.025). Notre estimation du taux de multiplication de la population λ est égale à 1.165 (SE = 0.036) pour les cerfs ayant reçu le traitement et 1.033 (SE = 0.038) pour les cerfs témoins. L'augmentation de survie des jeunes (i.e., survie fétale, néonatale et survie hivernale des faons) expliquait 64% de l'augmentation totale de λ, contre 36% pour l'augmentation de survie des femelles adultes. L'effet du traitement nutritionnel sur la survie hivernale des faons représentait à elle seule 33% de l'augmentation totale de λ.L'augmentation de λ en réponse à un supplément alimentaire nous a permis de mettre en évidence que la croissance de la population de cerfs de l'Uncompahgre est limitée par la ressource en nourriture. Nous avons montré que l'amélioration de la nutrition réduit les taux de prédation par le coyote (Canis latrans) et le puma (Puma concolor) sur les femelles adultes et les faons de plus de 6 mois. Nos résultats montrent que l'observation de prédation les coyotes n'est pas en soi utile pour déterminer si cette prédation a ou non un impact négatif sur une population de cerfs. Nos résultats indiquent également que, sous certaines circonstances, les pumas pourraient sélectionner les cerfs en mauvaise condition, ce qui suggère que la prédation par les pumas n'est probablement pas toujours une source de mortalité additive. Le taux de mortalité par maladie des femelles adultes n'a pas diminué en réponse à l'amélioration de la nutrition. La qualité de l'habitat dans l'aire de répartition hivernale est un facteur limitant la population de cerfs mulets du Plateau de Uncompahgre. Par conséquent, nous recommandons l'évaluation de traitements visant au retour des successions végétales et à l'accroissement de la productivité des habitats non-climaciques de pins/genévriers, lesquels dominent actuellement la répartition hivernale du cerf-mulet.
Our objectives in this study were to determine whether military activities (e.g., overflight noise, noise from ordnance delivery, ground-based human activity) on the Barry M. Goldwater Range (BMGR) affect the behavior and hearing of Sonoran pronghorn (Antilocapra americana sonoriensis). We contrasted the behavior of pronghorn on BMGR with the closest population of pronghorn in the United States that was not subjected to routine military activity (i.e., on the Buenos Aires National Wildlife Refuge [BANWR], Arizona). Forty percent of the landscape used by the endangered Sonoran pronghorn in the United States is within the 5,739 km2 BMGR, a bombing and gunnery facility in southwestern Arizona. The range of Sonoran pronghorn covers about 88% of BMGR. The 179 Sonoran pronghorn that lived in the United States in December 1992 declined to 99 by December 2000. The Sonoran pronghorn has been listed as endangered for >30 years, but population limiting factors are unknown. Because Sonoran pronghorn use BMGR, land and wildlife managers raised concerns about the potential effects of military activities on the population. Possible indirect effects of military activities on Sonoran pronghorn, aside from direct mortality or injury, from ordnance delivery, chaff, flares, live ammunition, aircraft mishaps, interference from ground vehicles and personnel, include alteration of behavior or physiology.We conducted the study on the North and South Tactical Ranges (NTAC and STAC), BMGR, from February 1998 to June 2000. Hearing exams were conducted in Camp Verde, Arizona, the University of Arizona, and on the East Tactical Range (ETAC), BMGR. Interactions between pronghorn and military activity were restricted to 4 observation points that provided viewing areas from which pronghorn and military activity could be observed from ≤ 10 km. We systematically located pronghorn with spotting scopes and telemetry. When located, we described their behavior and military activity using scan sampling. We tested hearing using auditory brainstem responses (ABR). We could not test the hearing of Sonoran pronghorn because of their endangered status, so we contrasted hearing of pronghorn near Camp Verde, Arizona, and desert mule deer (Odocoileus hemionus eremicus) that were and were not exposed to sound pressure levels from military activity. We recorded behavior observations of Sonoran pronghorn on 172 days (44,375 observation events [i.e., 1 observation/30 second]) over 373 hours. These data were compared with 93 days of behavioral data (24,297 observation events) over 202 hours for pronghorn not regularly influenced by military aircraft. Overall, we did not detect behavioral differences (i.e., time spent bedding, standing, foraging, traveling) between males and females. Pronghorn exposed to military activity, and those that were not, bedded the same amount of time. Pronghorn at BMGR foraged less and stood and traveled more than pronghorn not exposed to military activity. These trends were the same with and without anthropogenic activity. Only 7.3% of behavioral events occurred with identifiable stimuli. Military overflights occurred 363 times (0.8%) and non-military overflights occurred 77 times (<0.2%). Pronghorn rarely responded to military aircraft, but often moved >10 m when ground stimuli were present.Ambient noise levels ranged up to 123.1 decibels (dB). The average sound pressure level on days with military activity was 65.3 dB compared to 35.0 dB without military activity. Because we obtained hearing tests from deer and pronghorn, we were able to develop an ungulate weighting filter on the noise generated from overflights of A-10 and F-16 aircraft. Desert ungulates do not hear sound pressure levels generated from these aircraft as well as humans do (i.e., 14–19 dB lower).The military activity we examined had only marginal influence on Sonoran pronghorn. Pronghorn used the ranges shared with the military throughout the year and behavioral patterns of pronghorn were similar with and without the presence of military stimuli. Furthermore, pronghorn behavior exposed to military activity was similar to behaviors of pronghorn not exposed to regular military activity. The auditory characteristics of pronghorn were similar for those that have and have not been exposed to military activity. The population of Sonoran pronghorn in the United States continues to decline and is in serious danger of extirpation. Clearly, additional work needs to be done, but military activity as measured herein is not a limiting factor.
Invasions by nonnative plants have changed the structure of many terrestrial ecosystems and altered important ecological processes such as fire, the dominant driver in grassland ecosystems. Reestablishing fire has been proposed as a mechanism to restore dominance of native plants in grasslands invaded by nonnative plants, yet fire may function differently in these altered systems, potentially affecting animals in novel ways. To assess whether invasions by nonnative plants alter the effects of fire on animals, we performed a manipulative experiment in semi-desert grasslands of southeastern Arizona that have been invaded by a perennial, nonnative grass from Africa, Lehmann lovegrass (Eragrostis lehmanniana). We applied fire to 36 of 54 1-ha plots established along an invasion gradient where dominance of E. lehmanniana ranged from 0% to 91% of total live plant biomass. Over the 5-year period from 2000 to 2004, we used mark-recapture methods to assess how population and community attributes of small mammals varied along the gradient of nonnative grass and in response to fire. We quantified changes in presence of 17 species, abundance of 9 species, total abundance of all species combined, species richness, and species composition. Based on 11,226 individual mammals from 24 species, we found that effects of nonnative-grass dominance varied with habitat preferences of each species, resulting in composition of the small-mammal community changing predictably along the invasion gradient. As dominance of nonnative grass increased, presence and abundance of granivorous heteromyids and insectivores (e.g., Chaetodipus, Perognathus, Onychomys; pocket mice and grasshopper mice) decreased, whereas presence and abundance of omnivorous and herbivorous murids (e.g., Reithrodontomys, Sigmodon; harvest mice and cotton rats) increased. Species richness of the small-mammal community averaged 8.4 species per plot and was highest at intermediate levels of nonnative-grass dominance where vegetation heterogeneity was greatest. Abundance of all small mammals combined averaged 26.9 individuals per plot and did not vary appreciably with nonnative-grass dominance. During the 4- to 8-week period immediately after fire, abundance of 6 of the 9 most common species changed, with 5 species decreasing and 1 species increasing on burned plots relative to unburned plots. During this same time period, species richness of small mammals decreased by an average of 3 species (38%) and total abundance of all species combined decreased by an average of 16 individuals (61%) on burned plots relative to unburned plots. Effects of fire on vegetation biomass, on presence of 9 of 17 mammalian species, and on abundance of 4 of 9 mammalian species remained evident ≥2 years after fire. Effects of fire on most small-mammal species varied with the degree of nonnative-grass dominance, suggesting that fire functioned differently in areas invaded by nonnative plants relative to areas dominated by native plants. Specifically, effects of fire on presence of 12 of 14 species and abundance of 7 of 9 species varied along the gradient of E. lehmanniana. During this post-fire period, however, composition of the small-mammal community in areas dominated by nonnative grass transitioned towards composition of areas dominated by native grasses, suggesting that fires had some restorative effect on habitat for small mammals. The relative strength of this effect will likely depend in general on the structural and compositional contrasts between invaded and native plant communities. Despite the reported ineffectiveness of fire at reducing dominance of nonnative plants, restoring fire to grasslands invaded by nonnative plants can help maintain the mosaic of vegetation conditions necessary to support the diverse assemblage of animals that inhabit these fire-governed ecosystems. © 2011 The Wildlife Society.Invasiones por plantas no nativas han cambiado la estructura de muchos ecosistemas terrestres y alterado procesos ecológicos importantes tales como el fuego, el conductor dominante en ecosistemas de pastizales. El restablecimiento del fuego ha sido propuesto como un mecanismo para restaurar la dominancia de plantas nativas en pastizales invadidos por plantas no nativas, aun el fuego puede funcionar en forma distinta en esos sistemas alterados, potencialmente afectando a los animales en forma distinta. Para evaluar si las invasiones de plantas no nativas alteran los efectos del fuego sobre los animales, realizamos un experimento manipulativo en pastizales del semidesierto del sureste de Arizona que han sido invadidos por un pasto perene no nativo procedente de África, Lehmann lovegrass (Eragrostis lehmanniana). Aplicamos fuego a 36 de 54 parcelas de 1 ha establecidos a lo largo de un gradiente de invasión donde la dominancia de E. lehmanniana oscilo de 0 a 91% del total de la biomasa de plantas vivas. Sobre un periodo de 5 años desde 2000 hasta 2004, usamos métodos de marcaje-recaptura para evaluar como los atributos de la población y comunidad de pequeños mamíferos variaron a lo largo del gradiente de pastos no nativos y en respuesta al fuego. Cuantificamos cambios en la presencia de 17 especies, abundancia de 9 especies, abundancia total, riqueza de especies y composición de especies. Basado en 11,226 mamíferos individuales de 24 especies, encontramos que los efectos de la dominancia de pastos no nativos variaron con las preferencias de hábitat de cada especie, resultando en un cambio predecible de la composición de la comunidad de pequeños mamíferos a lo largo del gradiente de invasión. Conforme la dominancia de los pastos no nativos incremento, la presencia y abundancia de heterómidos granívoros e insectívoros (e.g., Chaetodipus, Perognathus, Onychomys) declinó, mientras que la presencia y abundancia de omnívoros y herbívoros múridos (e.g., Reithrodontomys, Sigmodon) incremento. La riqueza de especies de la comunidad de pequeños mamíferos promediaron 8.4 especies por parcela y fue la más alta a niveles intermedios de dominancia de pastos no nativos donde la heterogeneidad de la vegetación fue mayor. La abundancia de todo los pequeños mamíferos combinados promediaron 26.9 individuos por parcela y no varía apreciablemente con la dominancia de pastos no nativos. Durante el periodo de 4 a 8 semanas inmediatamente después del fuego, la abundancia de 6 de 9 de las especies más comunes cambiaron, con 5 especies declinando y una especie incrementando sobre las parcelas quemadas en relación a las parcelas no quemadas. Durante este mismo periodo de tiempo, la riqueza de especies de pequeños mamíferos declino por un promedio de 3 especies (-38%) y el total de la abundancia de todas las especies combinadas por un promedio de 16 individuos (-61%) sobre las parcelas quemadas en relación a las parcelas no quemadas. Los efectos del fuego sobre la biomasa de la vegetación, presencia de 9 de 17 especies de mamíferos, y abundancia de 4 de 9 especies de mamíferos permanecieron evidentes 2 ≥ años después del fuego. Los efectos del fuego sobre la mayoría de especies de pequeños mamíferos variaron con el grado de dominancia de pastos no nativos, sugiriendo que el fuego funcionó en forma distinta en áreas invadidas por plantas no nativas en relación a las áreas dominadas por plantas nativas. Específicamente, los efectos del fuego sobre la presencia de 12 de 14 especies y la abundancia de 7 de 9 especies variaron a lo largo del gradiente de E. lehmanniana. Durante este periodo después de la quema, sin embargo, la composición de la comunidad de pequeños mamíferos en áreas dominadas por pastos no nativos se convirtieron hacia la composición de áreas dominadas por pastos nativos, sugiriendo que el fuego tuvo algo de efecto de restauración sobre el hábitat para pequeños mamíferos. La fortaleza relativa de este efecto probablemente dependerá en general sobre los contrastes de estructura y composición entre comunidades de plantas invadidas y nativas. A pesar de la inefectividad reportada del fuego para reducir la dominancia de plantas no nativas, restaurando el fuego a pastizales invadidos por plantas no nativas pueden ayudar a mantener mosaicos de condiciones de vegetación necesarias para soportar la diversidad de grupos de animales que habitan esos ecosistemas gobernados por el fuego.L'invasion des plantes exotiques modifie la structure de nombreux écosystèmes terrestres et d'importants processus écologiques, tel le régime d'incendies qui façonne les écosystèmes des prairies. Le rétablissement des régimes d'incendies a été proposé pour restaurer la dominance des plantes indigènes dans les prairies envahies par des plantes exotiques, mais les incendies peuvent fonctionner différemment dans ces systèmes altérés et potentiellement affecter les animaux de nouvelles façons. Afin d'évaluer si les invasions de plantes exotiques modifient les effets du feu sur les animaux, nous avons effectué une étude expérimentale dans les prairies semi-désertiques du Sud-est de l'Arizona, qui ont été envahies par une graminée vivace exotique Africaine, Eragrostis lehmanniana. Nous avons incendié 36 des 54 parcelles de 1-ha établies le long d'un gradient où la dominance d'E. lehmanniana variait de 0 à 91% de la biomasse totale des plantes. Au cours de la période de 5 ans de 2000 à 2004, nous avons utilisé des méthodes de marquage-recapture pour évaluer comment les attributs des populations et communautés de petits mammifères variaient en fonction de l'abondance d'E. lehmanniana et en réponse au feu. Nous avons quantifié la variabilité de la présence de 17 espèces, de l'abondance de 9 espèces, de l'abondance totale, et de la richesse et composition des espèces. Basé sur 11,226 mammifères provenant de 24 espèces, nous avons trouvé que les effets de la dominance d'E. lehmanniana dépendait du choix d'habitat de chaque espèce, entraînant des changements prévisibles dans la composition de la communauté de petits mammifères. L'accroissement de la dominance de la graminée exotique entraîna une réduction de la présence et de l'abondance des hétéromyides granivores et insectivores (p. ex., Chaetodipus, Perognathus, Onychomys) et un accroissement de la présence et de l'abondance des muridés omnivores et herbivores (p. ex., Reithrodontomys, Sigmodon). La richesse des espèces de la communauté de petits mammifères était en moyenne de 8,4 espèces par parcelle, et était plus élevée aux niveaux intermédiaires de dominance d'E. lehmanniana, lorsque l'hétérogénéité de la végétation était la plus grande. L'abondance de tous les petits mammifères combinés était en moyenne de 26,9 individus par parcelle et n'était pas affectée de façon importante par la dominance de la graminée exotique. Au cours de la période de 4 à 8 semaines immédiatement après l'incendie, l'abondance de 6 des 9 espèces les plus abondantes changea, avec 5 espèces moins abondantes et 1 espèce plus abondante dans les parcelles brûlées que dans les parcelles non brûlées. Pendant cette même période, la richesse des espèces de petits mammifères diminua en moyenne de 3 espèces (38%) et l'abondance totale combinée de toutes les espèces diminua en moyenne de 16 individus (61%) dans les parcelles brûlés par rapport aux parcelles non brûlés. Les effets du feu sur la biomasse de la végétation, la présence de 9 des 17 espèces de mammifères et l'abondance de 4 de 9 espèces de mammifères sont restés évident ≥2 ans après l'incendie. Les effets du feu sur la plupart des espèces de petits mammifères variaient en fonction du degré de dominance d'E. lehmanniana, suggérant que le feu fonctionne différemment dans les zones envahis par des plantes exotiques comparé aux zones dominées par les plantes indigènes. En particulier, les effets du feu sur la présence de 12 de 14 espèces et l'abondance de 7 de 9 espèces ont varié sur le gradient d'E. lehmanniana. Cependant, au cours de cette période après-feu, la composition de la communauté de petits mammifères dans les zones dominées par la graminée exotique a convergée vers la composition des zones dominées par les graminées indigènes, suggérant que les incendies ont un effet restaurateur sur l'habitat pour les petits mammifères. La force relative de cet effet dépendra probablement en général des différences structurelles et compositionnelles entre communautés végétales envahies et indigenes. Malgré l'inefficacité signalée du feu pour réduire la dominance des plantes exotiques, le rétablissement des régimes d'incendies dans les prairies envahis par des plantes exotiques peut aider à maintenir la mosaïque des conditions végétales nécessaire pour supporter un assemblage diversifié des animaux qui peuplent les écosystèmes régis par les incendies.
Body condition has a strong influence on reproduction and survival. Consequently, understanding spatiotemporal variation in body condition may help identify processes that determine life history, and thus demography. The effect of environmental variables on individuals' body condition, although widely documented, is generally achieved by investigating habitat, plant phenology, or density separately, such that cumulative or interactive effects can rarely be considered. We investigated how spatial and annual variation in habitat composition, deer density, and vegetation productivity influenced white-tailed deer (Odocoileus virginianus) body condition during the breeding period. We detailed changes in body condition using several indices, including body mass, peroneus muscle mass, rump fat, kidney fat index, and antler size in >4,000 male and female deer of different ages harvested during September-December, 2002-2006 on Anticosti Island, Quebec, Canada. Overall, females and yearlings harvested in fir forests were in poorer condition than those harvested in peatlands or spruce forests, whereas body condition of adult males was greater when open habitats were highly available. High deer density reduced autumn gains in fat, muscle mass, and body mass in males and yearlings, and in fat for females. Surprisingly, density positively affected the size of male antlers. High density at birth favored fat accumulation in adult females, suggesting strong selective pressure that removed low-quality individuals in early age at high deer density. Low Normalized Difference Vegetation Index (NDVI) in spring was associated with delayed but rapid spring green-up, and favored higher body condition in autumn. Reproduction affected most parameters of body condition; lactating females had less mass, fat, and muscle than non-lactating females, whereas mass and fat of males >4 years old steeply declined during the rut. Body mass and fat reserves showed a stronger response to density, habitat, NDVI, and reproduction than muscle mass. Body mass was a good integrating measure of fat and muscle mass, although allocation between muscle growth and energy storage was confounded. Our study highlighted the influence of environmental conditions on individual fat reserves, muscle mass, and body mass in autumn, with potential effects on reproduction and winter survival. Appropriate monitoring of body-condition indices in the fall can track the effect of environmental variables and management practices on animal populations. (C) 2014 The Wildlife Society
Seasonal frequency of observed coyote group sizes, excluding pups <6 months old, on the Welder Wildlife Refuge, 1978-79.
Adult coyote intragroup relationships with pups at night on the Welder Wildlife Refuge, 1978-79.
Adult coyote intragroup relationships with pups during daytime on the Welder Wildlife Refuge, 1978-79.
Seasonal distances moved by 13 coyote pups during 57 24-hour periods on the Welder Wildlife Refuge, 1978-79.
The behavioral ecology of coyotes (Canis latrans) on the Welder Wildlife Refuge (WWR), South Texas, was studied from 17,556 telemetry locations of 63 coyotes and 844 visual observations of collared and uncollared coyotes from January 1978 through December 1979 and during May 1980, November 1980, and February 1982. Coyotes on the WWR were classified as 70% resident groups, 17% resident pairs, and 13% transients. Before whelping, each group (3-7 coyotes) consisted of a mated pair and associates. Seven mated pairs interacted frequently, maintained pair bonds for at least 3-20 months, and were most social during the breeding season. Breeders and associates interacted less than breeding pairs, and associates were seldom found with a breeder of the opposite sex if the other breeding individual was absent during the breeding season. Breeders and associates were active around pups, but did not alternate in attending pups. Adult coyote group size was not related to the percentage of time pups were left unattended. The percentage of time pups were together decreased as they matured. Composite home ranges, based on 95% of the locations, of 19 resident adult males (x = 4.7 km2) and 14 females (x = 4.3 km2) were similar. Home ranges of resident adult males and females did not differ within a season or among seasons. Home ranges, based on all locations, averaged 42.8 km2 for 10 male and 31.2 km2 for 11 female adult transients. Home ranges of coyote pups increased as they matured. Coyote pairs and groups occupied primarily contiguous, nonoverlapping home ranges with the larger home ranges of transients superimposed. Four adults were found within the same home range for 43-48 months and 4 pups for 9-29 months. Adult coyote home range areas were not related to group sizes. Annual percentages of emigration were 12-29% for adult males and 4-9% for adult females. Percentages of various-sized prey and white-tailed deer (Odocoileus virginianus) in coyote diets varied seasonally and were not related to the number of interacting coyotes living within home ranges nor to the average number of coyotes observed together. Although coyotes were most active during the night, daytime activity was noted. Activity patterns were similar for adult males and females, for residents and transients, and among seasons. Timing of activity periods by adults and pups were similar. Distances moved in 24 hours were similar for adult males (8.1 km) and adult females (7.8 km), and among other social classes, but distances moved were greatest during the breeding season with no relation to group size or foraging ecology. Distances moved by pups increased as they matured and were similar to those of adults during November-December. Five groups produced an average of 0.22 litter/km2 during both 1978 and 1979 and an estimated 1.4 pups/km2 in 1979. Annual mortality of adults averaged 32% and was higher for transients (49%) than residents (18%). Seven of 11 pups tagged when 1-5 months old died before 7 months of age. The relatively large groups of coyotes on the WWR likely resulted from habitat saturation and lack of human exploitation.
Microfilm. s Thesis (Ph. D.)--University of Washington, 1973.
The California spotted owl (Strix occidentalis occidentalis) is the only spotted owl subspecies not listed as threatened or endangered under the United States Endangered Species Act despite petitions to list it as threatened. We conducted a meta-analysis of population data for 4 populations in the southem Cascades and Sierra Nevada, California, USA, from 1990 to 2005 to assist a listing evaluation by the United States Fish and Wildlife Service. Our study areas (from N to S) were on the Lassen National Forest (LAS), Eldorado National Forest (ELD), Sierra National Forest (SIE), and Sequoia and Kings Canyon National Parks (SKC). These study areas represented a broad spectrum of habitat and management conditions in these mountain ranges.
Thesis (Ph. D.)--University of British Columbia, 1969. Bibliography: leaves 99-103. Microfilm. s
The endangered Axis porcinus in Royal Chitwan National Park is one of the principal prey species of the endangered Bengal tiger Panthera tigris. Sex ratio was 56 males:100 females. Groups of up to 20 deer were observed during February through April, after the first fires in the grasslands, but the basic social group consisted of an adult female and her juvenile offspring. The peak fauning season was March through April, but females gave birth from the end of January through April. Both males and females attained sexual maturity at about 15 months. Litter size was normally one, and 13 fawns/100 adults were observed. During all seasons, the deer fed in the mornings and evenings and bedded and ruminated during the hot part of the day. They were active during 41% of the day and 26-29% of the night. Home ranges overlapped extensively. Mean home ranges were estimated at 60 ha for females and 80 ha for males. Home range shape was dictated by food and water. Small home ranges indicated that hog deer were sedentary, preferring grasslands where food, cover, and water were available. Hog deer used grasslands almost exclusively. Grasses, ferns, semal Bombax ceiba flowers, and vellor Trewia nudiflora fruits were important food items. Saccharum spp., Imperata cylindrica and Cynodon dactylon composed 70% of the grass species available as food and cover. Tall grasses seem to be invading short grasslands, reducing available food for hog deer. -from Authors
Vital rates of large herbivores normally respond to increased resource limitation by following a progressive sequence of effects on life-history characteristics from survival of young, age at first reproduction, reproduction of adults, to adult survival. Expected changes in life history characteristics, however, should operate through changes in nutritional condition, which is the integrator of nutritional intake and demands represented primarily by the deposition and catabolism of body fat. Elucidating seasonal patterns of nutritional condition and its relative influence on individual and population performance should improve our understanding of life-history strategies and population regulation of ungulates, provide insight into the capacity of available habitat to support population growth, and allow assessment of the underlying consequences of mortality on population dynamics. We acquired longitudinal data on individual female mule deer (Odocoileus hemionus), and linked those data with environmental and population characteristics. Our goal was to provide a nutritional basis for understanding life-history strategies of these large mammals, and to aid in the conservation and management of large herbivores in general. We studied a migratory population of mule deer that overwintered in Round Valley on the east side of the Sierra Nevada, California, USA, and was subject to a highly variable climate and predation from a suite of large carnivores. We intensively monitored nutritional and life-history characteristics of this population during 1997–2009 as it recovered from a population crash, which occurred during 1985–1991. Deer in Round Valley migrated to high-elevation summer ranges on both sides of the crest of the Sierra Nevada (Sierra crest), where a rain shadow resulted in a mesic and more forested range on the west side compared with xeric conditions east of the Sierra crest. Average survival of neonatal mule deer to 140 days of age during 2006–2008 was 0.33 (SE = 0.091), but was lower for neonates on the west side (0.13, SE = 0.092) compared with those on the east side (0.44, SE = 0.11) of the Sierra crest. Birth mass and nutritional condition of mothers had a positive effect on survival of young; however, those effects were evident only for neonates born east of the crest where predation pressure was less intense compared with the west side. Black bear (Ursus americanus) predation was the main cause of mortality for west side young (mortality rate = 0.63, SE = 0.97) compared with canid and felid predation for east-side young (0.29, SE = 0.076). Mean autumn recruitment of young during 1997–2008 was lower for females on the west side (0.42, SE = 0.037) than for females on the east side (0.70, SE = 0.041) of the crest, and was affected positively by March ingesta-free body fat (IFBFat) of individual females. At the level of the population, ratios of young to adult females (1991–2009) were highly variable and strongly related to March IFBFat of adult females during the current and preceding year. Reproduction by yearling females was sensitive to per capita availability of forage during summer (as 1-yr-old individuals), thereby influencing whether a sufficient body mass for ovulation was obtained. Litter size remained high (1.69, SE = 0.027) during the study, but was influenced positively by forage availability, negatively by summer temperature, and was greater for females that resided on the west side of the Sierra crest during summer than those on the east side. In contrast, pregnancy rates remained unchanged across years of study (0.98, SE = 0.005). Survival of prime age (2–9-yr-old) females was 0.90 (SE = 0.021) in summer, 0.94 (SE = 0.012) in winter, and 0.87 (SE = 0.025) annually. Although relatively stable across years, both winter and summer survival were influenced positively by the preceding April snowpack relative to the density of the population. Mean IFBFat of adult females was 7.2% (SE = 0.077) in March 1997–2009 and 9.7% (SE = 0.23) in November 2002–2008. Nutritional condition offered a mechanistic link between factors that influence resource limitation and population performance, because condition of adult females in autumn and late winter was sensitive to the nutritional history of individual animals as related to forage growth, population density, migratory tactic, reproductive costs, and nutritional carryover. Nutritional condition of adult females in March also was the most parsimonious predictor of finite rate of population growth (λ) during the forthcoming year. The relative magnitude of effect of nutritional condition on survival and reproduction was mostly in accordance with the predicted changes of vital rates in response to resource limitation for populations of large herbivores. Our results indicated that management and conservation of large herbivore populations could be improved by integrating indices of nutritional condition into current monitoring and research programs. We offer a method to estimate the proximity of a population to nutritional carrying capacity (NCC) that is based on nutritional status of the population relative to population performance (termed animal-indicated NCC). The proximity of the population to animal-indicated NCC represents the short-term capacity of the environment to support population growth. A nutritional approach to monitor and manage populations offers a direct link to the capacity of the habitat, and reduces the need to estimate population abundance or set goals according to population size. We also propose that the consequences of mortality (degree of additive or compensatory mortality) on population dynamics can be assessed by comparing the estimated nutritional capacity for survival and recruitment of young to that measured empirically, because more young are produced than what the habitat can support when nutrition is limiting. Our approach is useful for quantifying effects of predation, and provides a basis for determining the efficacy of predator control to enhance ungulate populations.
DISSERTATION (PH.D.)--THE UNIVERSITY OF MICHIGAN Dissertation Abstracts International,
The federally threatened northern spotted owl (Strix occidentalis caurina) is the focus of intensive conservation efforts that have led to much forested land being reserved as habitat for the owl and associated wildlife species throughout the Pacific Northwest of the United States. Recently, however, a relatively new threat to spotted owls has emerged in the form of an invasive competitor: the congeneric barred owl (S. varia). As barred owls have rapidly expanded their populations into the entire range of the northern spotted owl, mounting evidence indicates that they are displacing, hybridizing with, and even killing spotted owls. The range expansion by barred owls into western North America has made an already complex conservation issue even more contentious, and a lack of information on the ecological relationships between the 2 species has hampered recovery efforts for northern spotted owls. We investigated spatial relationships, habitat use, diets, survival, and reproduction of sympatric spotted owls and barred owls in western Oregon, USA, during 2007-2009. Our overall objective was to determine the potential for and possible consequences of competition for space, habitat, and food between these previously allopatric owl species. Our study included 29 spotted owls and 28 barred owls that were radio-marked in 36 neighboring territories and monitored over a 24-month period. Based on repeated surveys of both species, the number of territories occupied by pairs of barred owls in the 745-km2 study area (82) greatly outnumbered those occupied by pairs of spotted owls (15). Estimates of mean size of home ranges and core-use areas of spotted owls (1,843 ha and 305 ha, respectively) were 2-4 times larger than those of barred owls (581 ha and 188 ha, respectively). Individual spotted and barred owls in adjacent territories often had overlapping home ranges, but interspecific space sharing was largely restricted to broader foraging areas in the home range with minimal spatial overlap among core-use areas. We used an information-theoretic approach to rank discrete-choice models representing alternative hypotheses about the influence of forest conditions, topography, and interspecific interactions on species-specific patterns of nighttime resource selection. Spotted owls spent a disproportionate amount of time foraging on steep slopes in ravines dominated by old (>120 yr) conifer trees. Barred owls used available forest types more evenly than spotted owls, and were most strongly associated with patches of large hardwood and conifer trees that occupied relatively flat areas along streams. Spotted and barred owls differed in the relative use of old conifer forest (greater for spotted owls) and slope conditions (steeper slopes for spotted owls), but we found no evidence that the 2 species differed in their use of young, mature, and riparian-hardwood forest types. Mean overlap in proportional use of different forest types between individual spotted owls and barred owls in adjacent territories was 81% (range = 30-99%). The best model of habitat use for spotted owls indicated that the relative probability of a location being used was substantially reduced if the location was within or in close proximity to a core-use area of a barred owl. We used pellet analysis and measures of food-niche overlap to determine the potential for dietary competition between spatially associated pairs of spotted owls and barred owls. We identified 1,223 prey items from 15 territories occupied by spotted owls and 4,299 prey items from 24 territories occupied by barred owls. Diets of both species were dominated by nocturnal mammals, but diets of barred owls included many terrestrial, aquatic, and diurnal prey species that were rare or absent in diets of spotted owls. Northern flying squirrels (Glaucomys sabrinus), woodrats (Neotoma fuscipes, N. cinerea), and lagomorphs (Lepus americanus, Sylvilagus bachmani) were primary prey for both owl species, accounting for 81% and 49% of total dietary biomass for spotted owls and barred owls, respectively. Mean dietary overlap between pairs of spotted and barred owls in adjacent territories was moderate (42%; range = 28-70%). Barred owls displayed demographic superiority over spotted owls; annual survival probability of spotted owls from known-fate analyses (0.81, SE = 0.05) was lower than that of barred owls (0.92, SE = 0.04), and pairs of barred owls produced an average of 4.4 times more young than pairs of spotted owls over a 3-year period. We found a strong, positive relationship between seasonal (6-month) survival probabilities of both species and the proportion of old (>120 yr) conifer forest within individual home ranges, which suggested that availability of old forest was a potential limiting factor in the competitive relationship between these 2 species. The annual number of young produced by spotted owls increased linearly with increasing distance from a territory center of a pair of barred owls, and all spotted owls that attempted to nest within 1.5 km of a nest used by barred owls failed to successfully produce young. We identified strong associations between the presence of barred owls and the behavior and fitness potential of spotted owls, as shown by changes in movements, habitat use, and reproductive output of spotted owls exposed to different levels of spatial overlap with territorial barred owls. When viewed collectively, our results support the hypothesis that interference competition with barred owls for territorial space can constrain the availability of critical resources required for successful recruitment and reproduction of spotted owls. Availability of old forests and associated prey species appeared to be the most strongly limiting factors in the competitive relationship between these species, indicating that further loss of these conditions can lead to increases in competitive pressure. Our findings have broad implications for the conservation of spotted owls, as they suggest that spatial heterogeneity in vital rates may not arise solely because of differences among territories in the quality or abundance of forest habitat, but also because of the spatial distribution of a newly established competitor. Experimental removal of barred owls could be used to test this hypothesis and determine whether localized control of barred owl numbers is an ecologically practical and socio-politically acceptable management tool to consider in conservation strategies for spotted owls.
Demographic data show many populations of Rocky Mountain (Cervus elaphus nelsoni) and Roosevelt (Cervus elaphus roosevelti) elk have been declining over the last few decades. Recent work suggests that forage quality and associated animal nutritional condition, particularly in late summer and early autumn, influence reproduction and survival in elk. Therefore, we estimated seasonal nutritional condition of 861 female elk in 2,114 capture events from 21 herds in Washington, Oregon, Wyoming, Colorado, and South Dakota from 1998 to 2007. We estimated ingesta-free body fat and body mass, and determined age, pregnancy status, and lactation status. We obtained estimates for most herds in both late winter–early spring (late Feb–early Apr) and in autumn (Nov–early Dec) to identify changes in nutritional condition of individuals across seasons.
We collected and chemically analyzed urine in snow (snow-urine) and simulated physiology of elk (Cervus elaphus) and bison (Bison bison) at the population level to assess changes in nutritional restriction, physical condition (i.e., fat reserves), and mortality rates on the Northern and Madison-Firehole ranges and at Pelican Valley in Yellowstone National Park during winters 1987-88 (1988) to 1989-90 (1990). On the Northern and Madison-Firehole ranges, elk diets vaned over the 3 winters with lowest consumption of grasses (P ≤ 0.006) and highest consumption of conifers (P ≤ 0.044) during the first winter post-fire (1989), which was also the most severe winter with respect to snow depth. Sedge use by Northern range elk also varied (P ≤ 0.002) with lowest use during pre-fire winter 1988 and greatest use during winter 1990; sedge use was stable at the more thermally-influenced Madison-Firehole range. Decreasing (P ≤ 0.014) mean urinary potassium:creatinine (K:C) ratios reflected progressive nutritional restriction on all sampling areas during all 3 winters. Mean urinary urea nitrogen:creatinine (UN:C) ratios of elk varied (P < 0.001) on the lower, middle, and upper Northern range and at Madison-Firehole during all 3 winters, except on the lower Northern range during winter 1989. Values of mean UN:C ratios and temporal trends indicated nutritional restriction was greatest during winter 1989, and restriction was increasingly severe from the lower to upper elevations of the Northern range and most severe at Madison-Firehole, where snow depths were greatest. On the Northern and Madison-Firehole ranges, bison use of grasses decreased (P ≤ 0.006) and sedges increased (P ≤ 0.005), while conifer use remained low and stable throughout the study. In Pelican Valley, bison food habits were unaltered during the study. Bison and elk diets were more similar at Madison-Firehole than on the Northern range, suggesting greater competition for food at Madison-Firehole. Mean K:C ratios of bison declined (P ≤ 0.014) throughout all winters on all sampling areas. Mean UN:C ratios increased (P ≤ 0.030) on the Northern, Madison-Firehole, and Pelican Valley ranges in each winter. Mean UN:C ratios were lower in bison than in elk, but temporal trends indicated that nutritional restriction of bison progressively increased each winter and was most severe during winter 1989. Measured UN:C ratios and herd composition were used by the physiological model to predict DEI on each range for bison and elk. At the predicted DEI on each range, there were spatial and temporal differences in fat reserves and mortality rates of elk and bison. The physiological model predicted that Madison-Firehole elk and bison were more severely nutritionally restricted and had lower fat reserves during winter 1989 than elk and bison on the Northern range. Lower fat reserves and higher winter mortality rates of elk and bison calves compared to cows predicted by the physiological model were consistent with the differential pressure exerted by density-dependent factors and amplified during the more severe winter.
Long-term wolf (Canis lupus) research programs have provided many insights into wolf population dynamics. Understanding the mechanisms controlling responses of wolf populations to changes in density, environmental conditions, and human-caused mortality are important as wolf management becomes increasingly intensive. Competition with humans for ungulate prey has led to large-scale wolf control programs, particularly in Alaska, and although wolf populations may sustain relatively high (e.g., 22–29%) rates of conventional harvest, control programs are specifically designed to have lasting population-level effects.
We reviewed the literature on factors potentially affecting the population status of American black ducks (Anas rupribes). Our review suggests that there is some support for the influence of 4 major, continental-scope factors in limiting or regulating black duck populations: 1) loss in the quantity or quality of breeding habitats; 2) loss in the quantity or quality of wintering habitats; 3) harvest, and 4) interactions (competition, hybridization) with mallards (Anas platyrhynchos) during the breeding and/or wintering periods. These factors were used as the basis of an annual life cycle model in which reproduction rates and survival rates were modeled as functions of the above factors, with parameters of the model describing the strength of these relationships. Variation in the model parameter values allows for consideration of scientific uncertainty as to the degree each of these factors may be contributing to declines in black duck populations, and thus allows for the investigation of the possible effects of management (e.g., habitat improvement, harvest reductions) under different assumptions. We then used available, historical data on black duck populations (abundance, annual reproduction rates, and survival rates) and possible driving factors (trends in breeding and wintering habitats, harvest rates, and abundance of mallards) to estimate model parameters. Our estimated reproduction submodel included parameters describing negative density feedback of black ducks, positive influence of breeding habitat, and negative influence of mallard densities; our survival submodel included terms for positive influence of winter habitat on reproduction rates, and negative influences of black duck density (i.e., compensation to harvest mortality). Individual models within each group (reproduction, survival) involved various combinations of these factors, and each was given an information theoretic weight for use in subsequent prediction. The reproduction model with highest AIC weight (0.70) predicted black duck age ratios increasing as a function of decreasing mallard abundance and increasing acreage of breeding habitat; all models considered involved negative density dependence for black ducks. The survival model with highest AIC weight (0.51) predicted nonharvest survival increasing as a function of increasing acreage of wintering habitat and decreasing harvest rates (additive mortality); models involving compensatory mortality effects received ≈0.12 total weight, vs. 0.88 for additive models. We used the combined model, together with our historical data set, to perform a series of 1-year population forecasts, similar to those that might be performed under adaptive management. Initial model forecasts over-predicted observed breeding populations by ≈25%. Least-squares calibration reduced the bias to ≈0.5% under prediction. After calibration, model-averaged predictions over the 16 alternative models (4 reproduction × 4 survival, weighted by AIC model weights) explained 67% of the variation in annual breeding population abundance for black ducks, suggesting that it might have utility as a predictive tool in adaptive management. We investigated the effects of statistical uncertainty in parameter values on predicted population growth rates for the combined annual model, via sensitivity analyses. Parameter sensitivity varied in relation to the parameter values over the estimated confidence intervals, and in relation to harvest rates and mallard abundance. Forecasts of black duck abundance were extremely sensitive to variation in parameter values for the coefficients for breeding and wintering habitat effects. Model-averaged forecasts of black duck abundance were also sensitive to changes in harvest rate and mallard abundance, with rapid declines in black duck abundance predicted for a range of harvest rates and mallard abundance higher than current levels of either factor, but easily envisaged, particularly given current rates of growth for mallard populations. Because of concerns about sensitivity to habitat coefficients, and particularly in light of deficiencies in the historical data used to estimate these parameters, we developed a simplified model that excludes habitat effects. We also developed alternative models involving a calibration adjustment for reproduction rates, survival rates, or neither. Calibration of survival rates performed best (AIC weight 0.59, % BIAS = -0.280, R2 = 0.679), with reproduction calibration somewhat inferior (AIC weight 0.41, % BIAS = -0.267, R2 = 0.672); models without calibration received virtually no AIC weight and were discarded. We recommend that the simplified model set (4 biological models × 2 alternative calibration factors) be retained as the best working set of alternative models for research and management. Finally, we provide some preliminary guidance for the development of adaptive harvest management for black ducks, using our working set of models.
Thesis (M.A. in Zoology)--University of California, Jan. 1963. "Food preferences of some East African wild ungulates" reprinted from the East African Agricultural and Forestry Journal, vol. 27, no. 3, January, 1962, l. 231. Bibliography: l. 203-220.
Canis lupus recolonized the Kenai Peninsula in the 1960s following a 50-yr absence. Wolf density ranged from 11-20 wolves/1000 km². Wolves fed primarily on moose Alces alces (density 0.8/km²); predation rate in winter averaged 1 moose/pack/4.7 days. Food consumption in winter was 0.12 kg/kg wolf/day, but intake apparently declined in summer. Calves composed 20% of the moose population but 47% of wolf-killed moose examined; proportionately more calves were killed during a winter with deep snow. Wolf predation selectively removed the oldest moose in the population. All but 3 of 72 wolf-killed adult moose of which sex could be ascertained were females. Typically 1 litter of wolf pups was born annually to the dominant female in each pack. Pups born to a socially subordinate female were growth-retarded and apparently died. Extraterritorial movements were most commonly undertaken by subordinate adult wolves during the February breeding season. Survival of dispersing wolves was only half that of nondispersers; most dispersers were killed before they could reproduce successfully. Mortality was largely human-caused, averaging 33% annually. Harvest increased rapidly, reducing pack size and causing declines in pack territory size. Additional packs developed in vacated areas, and total wolf density was maintained until annual kill exceeded 30-40% of the early winter population.-from Authors
Examined Canis lupus demography, movement patterns, predation characteristics in relation to migratory Rangifer tarandus granti. Wolf packs usually did not follow migratory caribou but maintained year-round resident territories that averaged 1 868 km2. However, during years when caribou were absent and moose Alces alces densities were low up to 17% of the radio-marked wolf packs followed migratory caribou and then returned to their original territory for denning. Radio-collared wolves dispersed primarily during April through September. Spring wolf densities increased from 2.7-4.4 wolves/1 000 km2 during 1987-1990, then declined to 1.5 wolves/1 000 km2 following a rabies epizootic. Annual wolf survival rates averaged 0.552 (range 0.464-0.656). Annual survival during 1990-91 and 1991-92 was lower than other years due to a rabies epizootic. Overall, hunting was the main cause of death (69%) for wolves (n=52). Most (63%) mortality occurred during December through March when snow cover permitted wolf hunting from snowmobiles. Caribou and moose composed 51 and 42%, respectively, of the kills observed during the study; 59% of caribou and 64% of moose kills were adult. Ungulate kills averaged 4.6/wolf/100 days and provided 5.3 kg of available food/wolf/day. When caribou densities were >200/1 000 km2, wolves switched to preying on resident moose. Wolves within the range of the Western Arctic Caribou Herd killed 6-7% of this caribou population annually. Caribou left wolf pack territories during winter, and wolves switched to preying on moose for c. 4 months of each year. Wolves killed 11-14% of the moose population annually. Wolf densities were limited by hunting and trapping, and wolf predation at levels found in 1987-91 did not strongly limit caribou population growth. However, existing wolf population may be able to regulate local, low-density moose populations that have become established during the past 40 yr.
River deltas have been presumed to provide high quality habitats for moose (Alces alces). Moose were introduced to the Copper River Delta, Alaska, in the 1950s, but little was known about their habitat relationships. This study was conducted during 1987-89 to characterize and evaluate moose habitat quality and moose ecology on a large river delta. Mean (±SE) annual home range size was 59 ± 5 km2. Eight of 15 radio-collared females and 1 of 4 males were seasonally migratory. Migrations were related to snow depth and persistence. Moose relocations (>90%) occurred in 5 habitat types, which were used either for feeding or bedding; use varied among years, seasons, and sexes. At the landscape scale, moose established home ranges in areas that had more habitats that were high in forage productivity and were relatively stable. At the home range scale, moose selected early seral habitats that provided both food and cover, or primarily cover. Spring-early summer diets were the most diverse and highest in quality due to the use of emergent aquatic plants. Winter diets were second in diversity and lowest in quality, and late summer-fall diets were the least diverse and intermediate in quality. Seasonal changes in diets, habitat selection, and activity budgets tracked changes in forage abundance and quality. The ecological carrying capacity of the study area was estimated to be 380 and 1,424 moose for severe and mild winters, respectively. These estimates would result in densities of 0.5-2.0/km2 for the entire area and 10-12/km2 on the primary winter ranges. The population could be increased beyond the present size to meet the high demands for moose. Calf production averaged 1 calf/female/year, the maximum twinning rate was 40%, mean annual calf survival rates ranged from 0.03 to 0.25, and fall recruitment averaged 30 calves/100 females. Calf deaths were associated with spring weather and predation by brown bears (Ursus arctos); >90% of adult mortality was due to legal harvest. Habitat quality on the Delta was dependent on disturbance regimes that differed in frequency and landscape extent. Glacial outwash dynamics produced a low variance, steady-state shifting mosaic over 30% of the Delta. Great earthquakes that occur every 600-800 years result in high variance, nonequilibrium habitat dynamics that currently favor moose.
Lesser snow geese (Chen caerulescens caerulescens) of the Western Canadian Arctic Population feed intensively for 2-4 weeks on the coastal plain of the Beaufort Sea in Canada and Alaska at the beginning of their autumn migration. Petroleum leasing proposed for the Alaskan portion of the staging area on the Arctic National Wildlife Refuge (ANWR) could affect staging habitats and their use by geese. Therefore we studied availability, distribution, and use by snow geese of tall and russett cotton-grass (Eriophorum angustifolium and E. russeolum, respectively) feeding habitats on the ANWR. We studied selection of feeding habitats at 3 spatial scales (feeding sites [0.06 m2], feeding patches [ca. 100 m2], and feeding areas [>1 ha]) during 1990-93. We used logistic regression analysis to discriminate differences in soil moisture and vegetation between 1,548 feeding sites where snow geese exploited individual cotton-grass plants and 1,143 unexploited sites at 61 feeding patches in 1990. Feeding likelihood increased with greater soil moisture and decreased where nonforage species were present. We tested the logistic regression model in 1991 by releasing human-imprinted snow geese into 4 10 × 20-m enclosed plots where plant communities had been mapped, habitats sampled, and feeding probabilities calculated. Geese selected more feeding sites per square meter in areas of predicted high quality feeding habitat (feeding probability ≥ 0.6) than in medium (feeding probability = 0.3-0.59) or poor (feeding probability < 0.3) quality habitat (P < 0.0001). Geese increasingly used medium quality areas and spent more time feeding as trials progressed and forage was presumably reduced in high quality habitats. We examined relationships between underground biomass of plants, feeding probability, and surface microrelief at 474 0.06-m2 sites in 20 thermokarst pits in 1992. Feeding probability was correlated with the percentage of underground biomass composed of cotton-grass (r = 0.56). Feeding probability and relative availability of cotton-grass forage were highest in flooded soils along the ecotone of flooded and upland habitats. In 1992, we also used the logistic regression model to estimate availability of high quality feeding sites on 192 80 × 90-m plots that were randomly located on 24 study areas. A mean of 1.6% of the area sampled in each plot was classified as high quality feeding habitat at 23 of the study areas. Relative availability of high quality sites was highest in troughs, thermokarst pits, and water tracks because saturated soils in those microreliefs were dominated by cotton-grass. Relative availability of high quality sites was lower in saturated soils of basins (low-centered polygons, wet meadows, and strangmoor) because that microrelief was dominated by Carex spp. Most (63%) of the saturated area on the ANWR coastal plain was in basins. We examined distribution of feeding patches relative to microrelief in 49 snow goose feeding areas in 1993. Only 2.5% of the tundra in each feeding area was exploited by snow geese. Snow geese preferentially fed in thermokarst pits, water tracks, and troughs, and avoided basins and uplands. Feeding areas had more thermokarst pit but less basin microrelief than adjacent randomly-selected areas. Thermokarst pits and water tracks occurred most frequently in regions of the coastal plain where geese were observed most often during aerial surveys (1982-93). Microrelief influenced selection of feeding patches and feeding areas and may have affected snow goose distribution on the ANWR. Potential feeding patches were widely distributed but composed a small percentage (≤2.5%) of the tundra landscape and were highly interspersed with less suitable habitat. The Western Canadian Arctic Population probably used a large staging area on the Beaufort Sea coastal plain because snow geese exploited a spatially and temporally heterogeneous resource.
Treatment and control areas for a study to determine the short-term impacts of a new section of United States Highway 64 on American black bears, Washington County, North Carolina, USA, 2000–2007.
Locations of hair snares on the treatment and control areas to determine short-term impacts of a new section of United States Highway 64 on American black bears, Washington County, North Carolina, USA, 2000 (preconstruction phase) and 2006 (postconstruction phase). We established hair snares during the postconstruction phase in the same locations as the preconstruction phase, except for sites where changes in forest cover or disturbance had occurred.
Percent inactivity of radiocollared American black bears for (A) morning (0400 hours through 1000 hours), (B) midday (1000 hours through 1600 hours), and (C) evening (1600 hours through 2200 hours) periods before (2000–2001) and after completion (2006–2007) of a new section of United States Highway 64, Washington County, North Carolina, USA. Vertical bars represent 95% confidence intervals and sample sizes represent individual bears.
Locations and reporting dates of American black bear mortalities from vehicle collisions on a new section of United States Highway 64, Washington County, North Carolina, USA, May 2007–November 2008.
Among numerous anthropogenic impacts on terrestrial landscapes, expanding transportation networks represent one of the primary challenges to wildlife conservation worldwide. Larger mammals may be particularly vulnerable because of typically low densities, low reproductive rates, and extensive movements. Although numerous studies have been conducted to document impacts of road networks on wildlife, inference has been limited because of experimental design limitations. During the last decade, the North Carolina Department of Transportation (NCDOT) rerouted and upgraded sections of United States Highway 64 between Raleigh and the Outer Banks to a 4-lane, divided highway. A new route was selected for a 24.1-km section in Washington County. The new section of highway included 3 wildlife underpasses with adjacent wildlife fencing to mitigate the effects of the highway on wildlife, particularly American black bears (Ursus americanus). We assessed the short-term impacts of the new highway on spatial ecology, population size, survival, occupancy, and gene flow of black bears. We tested our research hypotheses using a before-after control-impact (BACI) study design. We collected data during 2000-2001 (preconstruction phase) and 2006-2007 (postconstruction phase) in the highway project area and a nearby control area (each approx. 11,000 ha), resulting in 4 groups of data (i.e., pre-or postconstruction study phase, treatment or control area). We captured and radiocollared 57 bears and collected 5,775 hourly locations and 4,998 daily locations. Using mixed-model analysis of variance and logistic regression, we detected no differences in home ranges, movement characteristics, proximity to the highway alignment, or habitat use between the 2 study phases, although minimum detectable effect sizes were large for several tests. However, after completion of the new highway, bears on the treatment area became less inactive in morning, when highway traffic was low, compared with bears on the control area (F1, 43 = 6.05, P = 0.018). We used DNA from hair samples to determine if population size and site occupancy decreased following highway construction. For each study phase, we collected black bear hair from 70 hair snares on each study area during 7 weekly sampling periods and generated genotypes using 10 microsatellite loci. We used the multilocus genotypes to obtain capture histories for 226 different bears and used capture-mark-recapture models to estimate population size. Model-averaged estimates of population size decreased on the treatment area from 87.7 bears before construction to 31.6 bears after construction (64% reduction) and on the control area from 163.6 bears to 108.2 bears (34% reduction). Permutation procedures indicated this reduction was proportionally greater for the treatment area (P = 0.086). We also applied a spatially explicit capture-recapture technique to test our research hypothesis. The model with the most support indicated a greater change in density on the treatment area (69% reduction) compared with the control area (24% reduction). We did not observe a treatment effect based on survival of radiocollared bears. We used bear visits to hair snares as detections in multi-season occupancy models and found that occupancy decreased more on the treatment area (preconstruction: ψ = 0.84; postconstruction: ψ = 0.44; 48% decline) than the control area (preconstruction: ψ = 0.91; postconstruction: ψ = 0.81; 11% decline), primarily as a function of a greater probability of site extinctions (ε) on the treatment area (ε = 0.57) than the control area (ε = 0.17). Finally, individual-and population-based analyses of contemporary gene flow did not indicate the highway was a barrier to movements. Black bear use of the 3 wildlife underpasses was infrequent (17 verified crossings based on remote cameras, track surveys, and telemetry). Only 4 of 8 bears with home ranges near the highway were documented crossing the highway (n = 36 crossings), of which 2 were killed in vehicle collisions. Six additional bears were killed in vehicle collisions from May 2007 to November 2008, after we completed field work. Harvest data indicated that hunting mortality alone could explain the population decline on the control area. On the treatment area, however, hunting mortality only accounted for an approximately 40% population decline; the additional 30% decline we observed likely was caused by other mortality. We speculate vehicle collisions were primarily responsible. We conclude that impacts of the new highway on resident black bears occurred at the population level, rather than the individual or genetic level, but that the impact was smaller than harvest mortality. Increased activity by remaining bears when traffic volumes were low indicated behavioral plasticity. Bear use of the underpasses seemed sufficient to maintain gene flow between areas north and south of the new highway. Effectiveness of wildlife underpasses to reduce mortality of black bears may be enhanced if mitigation includes continuous fencing between crossing structures. For small, isolated populations of threatened or endangered large mammals, the potential demographic impacts of highways are an essential consideration in the transportation planning process. Control of mortality factors and maintaining demographic connectivity are particularly important.
Wildlife population estimators often require formal adjustment for imperfect detection of individuals during surveys. Conventional distance sampling (CDS) and its extensions (mark‐recapture distance sampling [MRDS], temporary emigration distance sampling [TEDS]) are popular approaches for producing unbiased estimators of wildlife abundance. However, despite extensive discussion and development of distance sampling theory in the literature, deciding which of these alternatives is most appropriate for a particular scenario can be confusing. Some of this confusion may stem from an incomplete understanding of how each approach addresses the components of the detection process. Here we describe the proper application of CDS, MRDS, and TEDS approaches and use applied examples to help clarify their differing assumptions with respect to the components of the detection process. To further aid the practitioner, we summarize the differences in a decision tree that can be used to identify cases where a more complex alternative (e.g., MRDS or TEDS) may be appropriate for a given survey application. Although the more complex approaches can account for additional sources of bias, in practical applications one also must consider estimator precision. Therefore, we also review the concept of total estimator error in the context of comparing competing methods for a given application to aid in the selection of the most appropriate distance sampling approach. Finally, we detail how the use of more advanced techniques (i.e., informed priors, open‐population distance sampling models, and integrated modeling approaches) can further reduce total estimator error by leveraging information from existing and ongoing data collection. By synthesizing the existing literature on CDS, MRDS, TEDS and their extensions, in conjunction with the concepts of total estimator error and the components of the detection process, we provide a comprehensive guide that can be used by the practitioner to more efficiently, effectively, and appropriately apply distance sampling in a variety of settings. We synthesize the existing literature covering the various distance sampling approaches and their extensions, in conjunction with the concepts of total estimator error and the components of the detection process. Through the use of applied examples, a decision tree, and detailed diagrams, we provide a comprehensive resource to help the practitioner efficiently select the appropriate distance sampling framework for a given survey application. A menudo los estimadores poblacionales de fauna silvestre necesitan ser modificados formalmente para la detección imperfecta de individuos durante un muestreo. El método convencional de medidas de distancia (CDS por sus siglas in inglés) y sus extensiones (el método de medidas de distancia con marca‐recaptura [MRDS] o con emigración temporal [TEDS]) son opciones populares para producir estimadores de abundancia de fauna silvestre sin sesgo. Sin embargo, a pesar de una discusión extensa y el desarrollo de la teoría y aplicación del método de medidas de distancia en la literatura, la decisión sobre cual opción es la más correcta para una situación en particular puede ser confusa. Algunas de estas confusiones surgen de un entendimiento incompleto de cómo cada opción define a los componentes del proceso de detección. Aquí describimos la aplicación correcta de CDS, MRDS y TEDS, y usamos ejemplos para clarificar sus diferentes supuestos en relación con los componentes del proceso de detección. Además, resumimos las diferencias de las 3 opciones en un árbol de decisión que se puede usar para identificar los casos que requieren de opciones más complicadas (p.ej., MRDS o TEDS). Aunque las opciones más complicadas pueden controlar las causas adicionales de sesgo, en las aplicaciones prácticas tenemos que considerar la precisión del estimador. Por consiguiente, examinamos el concepto de error total del estimador para comparar las diferentes opciones usando una aplicación específica que ayude a seleccionar el método de medida de distancias más apropiado. Por último, brindamos detalles de cómo el uso de métodos más avanzados (i.e., distribuciones previas informadas, modelos de medidas de distancia para poblaciones abiertas, y opciones de modelado integrado) pueden reducir el error total del estimador aprovechando la información de los datos de un muestreo en curso. Ofrecemos una síntesis de la literatura existente sobre CDS, MRDS, TEDS y sus extensiones, conjuntamente con los conceptos de error total del estimador y los componentes del proceso de detección, y proveemos una guía exhaustiva para aplicar el método de medidas de distancia apropiadamente en una variedad de situaciones.
Elk (Cervus elaphus) in the western United States are an economically and socially valuable wildlife species. They have featured species status for federal land management planning; hence, considerable modeling focused on habitat evaluation and land management planning has been undertaken for elk. The extent to which these and other habitat models for large ungulates account for influences of nutritional resources varies greatly, probably because of varying recognition of the importance of nutrition and uncertainty about how to measure and model nutrition. Our primary goals were to 1) develop greater understanding of how habitat conditions influence foraging dynamics and nutrition of elk in summer and autumn; and 2) illustrate an ecological framework for evaluating and predicting nutritional resources so that nutritional needs of elk can be integrated within landscape-scale plans, population models, and habitat evaluation models. We evaluated foraging responses of elk to clearcut logging and commercial thinning, forest succession, and season across ecological site potentials. We also identified the extent to which plant communities satisfied nutritional requirements of lactating female elk and their calves. Our study was conducted in the temperate rainforests of the Pacific Northwest on industrial and public timberlands.
Top-cited authors
Jeffrey L. Laake
Gary C White
  • Colorado State University
Chandler S. Robbins
  • United States Geological Survey
Rachel C. Cook
Bruce K Johnson
  • State of Oregon